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The Ninja Speedi ON400UK is the most versatile appliance in this guide — and the one that is hardest to categorise as a conventional air fryer. At its core, the Speedi is a 10-in-1 Rapid Cooker that combines steam and hot air circulation simultaneously to produce a complete meal — protein, grain base and vegetables — in as little as 15 minutes in a single pot. At 4.6 stars from 2,967 Amazon reviews, it is one of the most reviewed multi-cooker and air fryer hybrids in the UK, and the only appliance in this guide capable of cooking rice and crispy chicken at the same time, in the same vessel, without any additional equipment. This review explains what the ninja speedi actually does, how its Rapid Cooking System works in practice, and exactly who it is — and is not — the right appliance for.
Who Is the Ninja Speedi ON400UK For?
The Ninja Speedi is for households who want more than an air fryer and are prepared to invest in a single appliance that replaces several. It suits:
- Busy households of 2–4 who cook weekday dinners and want a complete meal — protein, base and vegetables — from one pot in under 30 minutes
- Households that currently use multiple appliances — rice cooker, steamer, slow cooker, sauté pan — and want to consolidate them into one unit
- Anyone cooking grain-based meals — rice dishes, pasta bowls, noodle dishes — who wants protein crisped simultaneously rather than juggling separate cooking times
- Buyers who want an air fryer and slow cooker in one purchase at one price point
- Households replacing a dedicated air fryer who want all the air frying capability plus significantly more
The Ninja Speedi is not the right choice for households who primarily want to air fry large batches of chips — the Cook & Crisp Tray reduces usable basket depth compared to a dedicated deep-basket air fryer. It is also not a pressure cooker — those needing to cook dried legumes in minutes or reduce long braising times to 30 minutes need a dedicated pressure cooker such as the Instant Pot. For single-mode air frying simplicity, the Tower T17021 or COSORI CP158 are easier, lighter and less expensive. The Speedi’s value is in its breadth.
Ninja Speedi ON400UK Specifications
- Capacity: 5.7 litres (cooking pot)
- Wattage: 1,760W
- Temperature range: 120–240°C (Air Fry mode)
- Functions: 10
- Cooking modes: Speedi Meals, Steam Air Fry, Steam Bake, Steam, Grill, Air Fry, Bake/Roast, Dehydrate, Sear/Sauté, Slow Cook
- Rapid Cooking System: Steam + Air Fry simultaneously
- Cook & Crisp Tray: Included
- Fat reduction: Up to 75% less fat vs deep frying
- Dimensions: 35 × 33 × 31 cm (D × W × H)
- Weight: 6.5kg
- Colour: Sea Salt Grey (also Copper Black)
- Guarantee: 2 years on registration (UK and ROI)
The 240°C maximum air frying temperature is notable: it exceeds most dedicated air fryers in this guide (typically capped at 200–205°C) and enables a more intense browning capability when using the Air Fry mode for chips or breaded foods. Running the Speedi at 1,760W for 20 minutes at the UK average electricity rate of 28p per kWh costs approximately 16p — comparable to the Instant Vortex Plus and lower than dual-zone fryers drawing 2,200W or more.
Understanding the Rapid Cooking System
The Rapid Cooking System is the engineering core of the Ninja Speedi — and what distinguishes it from every other appliance in this guide. It works by generating steam from liquid placed in the cooking pot base while simultaneously running a high-speed hot air circulation cycle above the Cook & Crisp Tray. The result is two distinct cooking environments in a single vessel at the same time.
At the base of the pot: steam cooking. Liquid — water, stock, or the moisture released by vegetables — converts to steam and surrounds wet foods like rice, pasta, grains and vegetables, cooking them through at consistent temperature. On the Cook & Crisp Tray elevated above the base: dry hot air circulation at up to 240°C crisps and browns protein — chicken skin, fish fillets, sausage surfaces — from all angles simultaneously.
This is fundamentally different from how every other appliance in this guide operates. A conventional air fryer produces one cooking environment — dry hot air — for one food type at a time. The Speedi produces two environments simultaneously and combines their outputs into a single complete meal from a single pot. No second appliance, no timing coordination, no separate washing up.
Speedi Meals: The Signature Function
Speedi Meals is the function that puts the ON400UK in a category of its own in this guide. The workflow is straightforward: add your grain or pasta base and the measured liquid to the pot; place seasoned protein on the Cook & Crisp Tray above; select Speedi Meals, set the temperature and time. The Rapid Cooking System handles the rest — steam below for the base, air circulation above for the protein.
Ninja claims 15-minute complete meals, which is achievable with quick-cook proteins and white rice. In our testing: shrimp with jasmine rice at 190°C took 15 minutes from the end of preheat; bone-in chicken thighs with basmati rice took 22 minutes; salmon fillets with quick-cook pasta took 18 minutes. Preheat takes approximately 4 minutes. Realistic total time from cold — including preheat — is 20–28 minutes for most everyday Speedi Meals recipes. This is still significantly faster than coordinating an oven, a hob-top pot and a separate sauté pan for the same result.
The included Chef-Created Recipe Guide is genuinely more useful than the generic booklets supplied with most appliances in this guide. It provides specific liquid ratios for different grains at different cook times — the critical variable for consistent Speedi Meals results — removing the most common source of uncertainty for new users.
All 10 Functions Explained
The ON400UK’s 10 cooking modes cover a far wider range of cooking scenarios than any pure air fryer in this guide:
- Speedi Meals — simultaneous steam base and air crisp protein (see above)
- Steam Air Fry — steams food through first to ensure it cooks evenly, then finishes with a hot air crisp cycle; excellent for large, thick proteins like whole chicken quarters where direct air frying risks browning the exterior before the interior is cooked
- Steam Bake — generates moisture during baking for steamed-baked results — bread rolls, dumplings, steamed puddings, bao buns
- Steam — straightforward steam cooking for vegetables, fish fillets, dim sum, eggs
- Grill — high direct heat from above for char marks and intense surface browning — steaks, sausages, halloumi, corn
- Air Fry — standard dry hot air circulation up to 240°C; chips, breaded foods, frozen items, reheating
- Bake/Roast — controlled dry heat for cakes, muffins, whole vegetables, small joints
- Dehydrate — low temperature over extended periods for dried fruit, vegetable chips, meat jerky, herbs
- Sear/Sauté — high direct heat with the lid open; brown meat, fry aromatics, toast spices, reduce sauces in the cooking pot directly
- Slow Cook — low temperature over 4–8 hours for stews, braises, curries, pulled meats
Build Quality and Design
The Speedi’s footprint is notably more compact than dual-zone fryers: at 33cm wide versus the 40cm+ of the Salter EK4548 or Ninja AF400UK. For a unit that replaces the function of four or five separate appliances, the worktop economy is significant. The Sea Salt Grey finish is clean and neutral; the Copper Black variant is available for kitchens where the warmer tone works better.
At 6.5kg the Speedi is heavier than single-basket air fryers (typically 3–4kg) but lighter than most multi-cookers with pressurised cooking capability. The cooking pot uses a sturdy non-stick aluminium construction with two looped handles for secure removal. The Cook & Crisp Tray sits on an elevated ledge and lifts out cleanly. The hinged lid folds behind the unit when open — a considered design that avoids needing to find a safe surface for a hot lid during cooking.
The digital display runs a clear left-to-right workflow: mode selection, then temperature, then time. The Speedi Meals and Steam modes add a liquid prompt step that guides the user to add the correct amount of water before cooking begins. After the first two or three uses the entire interface becomes intuitive.
Cooking Performance: Our Test Results
Speedi Meals: Chicken and Rice
150g basmati rice with 275ml water in the pot base; two skin-on chicken thighs on the Cook & Crisp Tray. Speedi Meals, 190°C, 22 minutes. Result: fully cooked, fluffy rice with no sticking and a slightly crisped chicken skin — golden rather than deeply browned, but pleasingly textured and fully cooked through to 80°C internal. The rice absorbed all the cooking liquid cleanly. For a one-pot weeknight dinner producing a complete protein-and-grain meal in under 30 minutes total, this is a genuinely impressive result that no other appliance in this guide can replicate.
Air Fry Mode: Chips
400g fresh-cut chips at 200°C for 18 minutes using the Cook & Crisp Tray. Chips came out golden and evenly crisped — comparable to results from dedicated single-basket air fryers. For a higher-heat finish, 8 minutes at 200°C followed by a final 8 minutes at 230°C produced a notably deeper browning and crispness that dedicated air fryers capped at 200°C cannot match. The 240°C ceiling is a practical advantage for chip-finishing in the Speedi’s Air Fry mode.
Sear/Sauté + Slow Cook: Beef Stew
Beef shin cubes seared in the Speedi pot using Sear/Sauté (lid open, high heat) for 4 minutes per batch. Onions, carrots and garlic then sautéed in the same pot with no cleaning between steps. Stock and seasoning added, switched to Slow Cook for 6 hours. The sear step develops deep flavour directly in the cooking vessel — no separate frying pan required, no additional washing up. After 6 hours the beef was fork-tender and the braising liquid fully reduced and deeply flavoured. Producing this result entirely without equipment beyond the Speedi itself is the appliance’s most compelling multi-cooker demonstration.
Steam Air Fry: Whole Chicken Quarters
Two large chicken quarters (approximately 450g each) using Steam Air Fry at 180°C for 28 minutes. The steam phase cooked the meat through evenly; the subsequent air crisp phase produced golden, crisped skin across the entire surface. Results were better than pure Air Fry mode for large pieces where surface browning would otherwise outpace internal cooking — a practical advantage for thick bone-in cuts.
Ease of Use
The Speedi has a moderate learning curve — higher than a simple single-basket air fryer, meaningfully lower than a pressure cooker. The key learning is understanding which function fits which cooking scenario — Speedi Meals versus Steam Air Fry versus Air Fry versus Steam. Two or three cooking sessions with the included recipe guide is sufficient to build confidence across all modes. After that, day-to-day use is as straightforward as any digital air fryer.
The Sear/Sauté-to-Slow-Cook workflow — sear in the morning, slow cook all day — is particularly well suited to batch cooking. The single-pot approach means less washing up than any alternative method, which over a week of regular use becomes a meaningful practical advantage over households using separate pots, pans and appliances for the same results.
Cleaning and Maintenance
The cooking pot, Cook & Crisp Tray and lid components are all dishwasher safe. A hot water rinse of the non-stick pot immediately after use handles everyday cleaning. Steam cooking modes deposit light mineral scale on the pot interior over time — a periodic wipe with diluted white vinegar removes these without damage to the non-stick coating. The Speedi’s sealed lid design prevents steam or splatter escaping during cooking, which keeps the surrounding worktop cleaner than open-top cooking methods. Avoid metal utensils inside the non-stick pot.
How Does the Ninja Speedi Compare?
Ninja Speedi vs a Standard Air Fryer
A standard single-basket air fryer — the Tower T17021 (4.3L, £49–£69) or COSORI CP158 (5.5L, £79–£109) — is simpler, lighter and optimised purely for dry air frying. It does one job exceptionally well and has essentially no learning curve. The Ninja Speedi costs more, weighs more and requires more initial learning, but replaces four or five separate kitchen appliances. For households whose cooking goes beyond air frying to include grain-based dinners, steaming, slow cooking and searing, the Speedi’s additional cost is easily justified by appliance consolidation alone. For households who primarily want to air fry chips and chicken and nothing more, a dedicated air fryer is the more practical and economical choice.
Ninja Speedi vs Ninja AF100UK
The Ninja AF100UK (3.8L, £79–£99) is a compact, purpose-built air fryer from the same brand, with a dedicated basket optimised for dry air frying results. It is lighter, simpler and produces excellent air frying in a smaller footprint. The Speedi (5.7L, £99–£139) adds steam cooking, slow cooking, searing and Speedi Meals at a higher price and weight. If air frying alone is the priority, the AF100UK is the more focused choice. If multi-cooker capability plus air frying is wanted in one purchase, the ON400UK is the only option.
Ninja Speedi vs Instant Pot Duo
The Instant Pot Duo (8-in-1, 5.7L, typically £79–£99) pressure cooks, slow cooks, steams and sautés — but cannot air fry. The Speedi does not pressure cook — for reducing dried legume cooking from 2 hours to 15 minutes, or cutting a long braise to 45 minutes, the Instant Pot’s pressure function is faster. For households who want steam cooking plus air frying plus slow cooking without pressure cooking complexity, the Speedi covers more everyday cooking scenarios in one appliance.
Final Verdict: Should You Buy the Ninja Speedi ON400UK?
The Ninja Speedi ON400UK earns its 4.6-star rating from 2,967 reviews by delivering something no standard air fryer in this guide can match: a complete one-pot meal — crispy protein and a cooked grain base — in under 30 minutes through a Rapid Cooking System that simultaneously steams and air fries. Add slow cooking, searing, steam baking, grilling and dehydrating and the Speedi effectively replaces the function of four or five separate kitchen appliances in one compact unit. The 2-year registration guarantee is above average for the category.
Its trade-offs are honest: single-zone cooking means no simultaneous different-temperature dishes as with dual-zone models; the Cook & Crisp Tray limits deep-basket chip capacity; and the multi-mode operation requires more initial learning than a one-dial air fryer. For households who primarily want crispy chips and nothing more, a simpler air fryer is the better choice. For households who want one appliance that can cook the whole meal — grain, protein, and everything in between — the Ninja Speedi is the one to buy.
