they don't do a good job. but they do get it done quicker.
the bowl trimmer is better used wet. you'll mutilate larger chunks of bud if dry. i've put a few pounds through it. kept blad clean and hasn't dulled yet. still cared to touch that thing, lol, defintely going to cut myself at some point. If you can get a larger one cheaply, increased surface area scales up quickly. 24" is 177% larger than an 18" version - fewer fill ups to get done. i wouldn't worry about name brand on a bowl trimmer because they are all imprecise. this was a couple years ago, but found a 24" version for 175ish? Read reviews and make sure it's not some dud manufacturer, but otherwise these are all essentially the same.
tumblers might give a closer shave. probably knock off a bit more beyond leaf too, but not too much. Unless it has blades, will need dry buds. can always collect anything good lost for re-use. Compared to the bowl where the blade is behind a grate and only what sticks through more than 1/8" or more will get lopped off, the cause of the trimmingis coming in direct contact with the buds. probably does a better job as far as leaving less behind, but also takes off more good stuff.
some of those have blades as part of it... some it's just hitting side of contaner with hexagonal holes and friction pulls off the leaves. they get expensive. Can probably DIY something similar.
weedbag thing with a spiral blade or whatever inside == again, probably tighter than a bowl trimmer, but beats the shit out of your weed, lol.
the better job it does, the more waste is likely invovled. Can of course do something with the trim to recoup the waste