1. Steel body vs plastic body — the most important spec line on this list
Both Philips and Breville air fryers use plastic outer bodies. Crumble uses steel. This is not a cosmetic difference — it’s a material difference that affects how the appliance looks, how it ages, and what it smells like when it heats up.
Plastic bodies degrade. They yellow, crack at the seams, and produce that characteristic plastic-and-heat smell that signals chemistry you’d rather not be near. Steel doesn’t do any of that.