They do ok, for me tho, if it was headstash, I'd trim by hand, if for commercial use, I'd use trimmer and save time have less need for extra scissors, but imo the lower end trimmers (only ones I've used) do need a bit of clean up if you want A grade look otherwise it does good enough to pass as trimmed but u might get a few complaints.
But the best part of using the trimmers is right after you clean them, the finger/trimmer hash is soooooo good! On second thought, maybe using for headstash too...