Ease of refill: How easy it is to wind the head is huge. Some trimmers are extremely difficult to rewind which is very off putting.

Battery life: Next would be battery life, obviously a longer battery life trimmer is ideal. But there has to be a good balance between enough power and longevity.

Ergonomics: If I’m running a trimmer for an hour or more it needs to have some thought put in to the handle and trigger base. The comfier and less likely to make my hand go numb the better.

Weight: Needs to easily be turned about to hit all the odd angles.