USB-rechargeable or cordless operation (so it’s truly portable).
Food-grade stainless-steel blades.
Safe materials (BPA-free plastics or good quality ABS/PP plastic).
A container size that suits your needs (if you chop a lot of vegetables vs just garlic/chilli).
Easy cleaning / removable parts.
Clear specification of what “4-in-1” or “multi-function” means (slicing, chopping, mincing, etc).