The Ninja SL451UK and SL400UK share the Double Stack XL format, but their similar names can hide an important difference: the SL451UK includes a digital cooking probe. Compare the exact model and included accessories before treating two prices as equivalent.
This guide uses the manufacturer's specifications and current catalogue listings. We have not tested either appliance, and do not assign cooking-performance scores or claim that one always offers the best value.
See the at-a-glance comparison above ↑
The official SL451UK page and SL400UK page support these specifications. Retailer bundles and condition can vary, so check the box contents on the offer you select.
When is the SL451UK worth considering?
Choose around how you cook, rather than the length of the model name. The included probe is the clearest specification difference here. If you want it, compare the SL451UK package with the complete alternative package you would otherwise buy; do not assume an optional probe works with every model.
If you mainly want the stacked-drawer layout, compare current delivered prices first. Paying more for an accessory you do not expect to use may not help you. Conversely, a similar price for the SL451UK can make its additional equipment relevant to your decision.
Will a Double Stack fit your worktop?
The narrow body still needs a deep enough worktop. Measure the width, depth and height, then allow the clearance required in the instructions for the exact appliance. Also consider room to pull drawers out and somewhere to put hot removable parts safely.
Do not interpret total capacity as a promise that your usual meal will fit. Think about the shape of the food and how you would divide it between drawers and racks. Look at the manufacturer's cooking guidance before deciding whether the arrangement suits your household.
Avoid comparing a different Double Stack
“Double Stack” is a family name. Check SL451UK or SL400UK in the selected listing rather than assuming every result has the same capacity or contents. A cookbook, replacement drawer or rack is not a complete air fryer.
Our Double Stack comparison page provides another way to browse current listings. For other layouts and brands, use the air-fryer collection, including its stacked and dual-basket controls.
Check cleaning and retailer terms
The manufacturer's standard specifications list removable drawers and crisper plates as dishwasher-safe. Follow the instructions for each part; that does not mean the powered appliance or every accessory can go in a dishwasher. Make sure a used or refurbished offer includes the parts you expect.
Before buying, compare the exact model, condition, delivery charge, guarantee requirements and returns. Prices in the comparison components update separately from this guide. A current retailer reduction is not proof of a historical low or a Black Friday saving.
Quick answers
Does SL451UK mean a bigger capacity than SL400UK?
No. Both models in this comparison have a stated total capacity of 9.5 litres. The included digital cooking probe is the key equipment difference described here.
Which one should I buy?
Start with the probe requirement and the space available in your kitchen. Then compare complete packages for the same condition and final delivered price. This guide does not declare a universal winner.
