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The Ninja DoubleStack SL400 is a good fit if you want two cooking zones and generous stated capacity without giving up as much counter width as a side-by-side air fryer. Its 9.5L is divided between two 4.75L drawers, but the tall, deep design still needs space, and its narrow cooking shape will not suit every large food. In reviewer Laura Honey’s tests, some foods browned unevenly unless shaken or turned midway, so it works best for cooks willing to intervene rather than load a drawer and leave it alone.
What the Ninja DoubleStack SL400 offers
The SL400 has two vertically stacked drawers, each rated at 4.75L, for 9.5L combined capacity. Ninja UK lists six cooking functions: Air Fry, Max Crisp, Roast, Bake, Dehydrate and Reheat. The UK specification also lists 2470W, a weight of 10.3kg and dimensions of 38.5cm high × 28cm wide × 47cm deep. These are manufacturer specifications for the UK SL400UK, not guarantees that every regional version has identical electrical details or accessories. Ninja UK’s SL400UK product page has the regional listing.
The UK model is called the DoubleStack XL; Ninja Australia calls its SL400 the DoubleStack XXXL. The Australian product page describes Smart Finish, which coordinates two foods with different settings to finish together, and Match Cook, which copies settings across both zones. Check your local model listing for feature names and included items before buying; regional naming and configurations should not be assumed to match exactly. Ninja Australia’s SL400 page describes those functions.
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The main performance qualification in Laura Honey’s Woman & Home review is uneven browning when food is left undisturbed. In one test, chips cooked for 20 minutes at 200°C without shaking were close to burning at the front while less cooked at the rear. A second batch cooked for 16 minutes with a halfway shake came out well. Fish fingers also browned more at the front than at the rear and needed extra time. These are results from one reviewer’s tests, not proof that every batch or food will behave the same way. They do show why it is sensible to check and redistribute food during cooking. Read Honey’s full review.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
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Other foods fared well with attention to placement and timing. Honey reported well-browned roast vegetables, a successful rice-and-tofu bowl, and brownies that baked through but were lighter than her preferred fudgy texture. Small vegetable pieces caught in the grate. The range of functions and rack arrangement make the appliance versatile, but outcomes depend on what is being cooked and how it is arranged.
Practical habits for more even results
- Shake or turn foods such as fries partway through, and move pieces between the front and rear if browning differs.
- Check delicate or unevenly sized foods before the programmed time ends; the fish-finger test needed additional cooking at the rear.
- Leave room for air to circulate rather than packing a drawer to its nominal capacity.
Does the stacked design save counter space?
It saves width compared with a conventional side-by-side dual-basket layout, but it is not a compact appliance in every direction. At 38.5cm tall and 47cm deep on the UK specification, it may project a long way from the wall or be awkward under low cupboards. Honey also found the side-mounted control panel fiddly to accommodate when positioning it. Measure the intended location, including clearance for ventilation and access to the controls, rather than judging fit by width alone.
Rank #2
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The two 4.75L drawers are flexible for separate foods, but capacity is not the same as usable cooking shape. A large flat item such as an uncut pizza may not fit whole. TechRadar’s 2026 buying guide similarly cautions that the maker’s eight-portion claim feels ambitious. Honey estimated four to six people based on her experience; that is a reviewer’s assessment, not a fixed serving limit. TechRadar’s 2026 air-fryer guide discusses the model’s capacity and shape.
Controls, racks and cleaning
Ninja UK lists two non-stick drawers, two crisper plates and two multi-layer racks among the included items, along with the main unit and instruction booklet. The extra rack positions are useful when cooking several types or layers of food, but they do not remove the need to check and move food where browning is uneven. Confirm the accessory list for the exact regional SKU you are considering.
Rank #3
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- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Ninja describes components as dishwasher-safe, while Honey found hand-washing the non-stick drawers straightforward. She did find vegetable debris lodged in the rear grate, which took extra effort to remove. Do not assume that every component is dishwasher-safe: follow the care instructions for the specific part in your model’s manual. A silicone utensil can help lift food from the grate, but it is not listed as an included accessory.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Should you buy it instead of a side-by-side dual-basket fryer?
Choose the SL400 if preserving counter width matters, you value two zones for different foods, and the stacked drawers suit the shape of what you cook. Look elsewhere if you often cook large flat foods whole, need a shorter or shallower unit, or want to minimize mid-cook shaking and rearranging.
Rank #4
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Value depends on current local pricing. TechRadar describes the DoubleStack as expensive relative to dual-basket alternatives. Honey notes that Ninja’s larger, side-by-side AF400 can offer more capacity and performance for less money, at the cost of more counter width. Treat that as her review comparison, not a live price guarantee; prices change, and the relevant choice is the trade-off between width, usable drawer shape, performance and cost.
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Honey called the DoubleStack “perfect” for a small kitchen feeding a whole family, but that is her review opinion rather than an objective promise about fit or portions. The more practical test is whether its measured height and depth fit your kitchen and whether the drawer dimensions match the food you typically cook.
Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
