I think you'll find there really isn't one so much better than another that we can call one the best. Each one will trim a case to normally the spec's. you want if you used it right. I've used this one, a very old R.C.B.S, a very old Lyman and one other I don't recall the name of. They all did what they were supposed to do, IF, I did my part right! So, do you simply want to spend money on a power trimmer thinking you got the best or could you be happy turning a crank handle? Either way you'll get the right length if you do your part right. Reason for so many people using old manual trimmer's. My reason is I'm cheap and don't want to spend more money just to do the same job maybe faster!
Lot of people go to the auto trimmer and generally auto other tools at the same time as they want higher production. Well if that it for you, go for the auto trimmer, probably work well which every one you get.
