Since I started loading in '65 I've seen and used several trimmers. Perhaps the "best" was a Wilson in that it was quite repeatable and cut the mouths absolutely square.
Those trimmers with stepped, "draw-in" type collets are pretty much all the same. The finished lengths are somewhat dependant on the diameter of the individual case rims. Not all are the same diameter and lengths vary accordingly.
I suggest avoiding any case trimmer using standard shell holders to secure the cases in place. They all index off the forward face of the case rims so finished lengths will vary by however much the rim thicknesses vary.
A "Handloader's Digest" back in the late 60s or early 70s gave a good report on the new, at that time, Lyman "Universal" trimmer. I took that advice and mine has worked great for me.
The Lyman's "Universal" name comes from the fact it has a universal case holder system, no case collets required. And it comes with nine caliber pilots as part of the basic package. That universal case holder draws the case head back firmly against a steel stud so finished case lengths are consistant. It has a good (but un-calibrated) coarse/fine length adjustment nut on the cutter shaft, works as good or better than any other brand.
Lyman has several accessories that make their trimmer more versatal than any other I know of; an outside neck turner, primer pocket cleaners and uniformer and GI crimp remover, a champher/deburr tool, etc. Over all, it is a pretty good system for sporter rifles. It's not up to bench rest competition standards but neither are any of the trimmers available from our standard handloading tool makers.
You will also require a decent machinist's caliper for measuring lengths. An inexpensive 6" stainless steel dial caliper from Harbor Freight Tools costs maybe $16-18 when on sale, and they frequently are. I think all of the common reloader calipers are from the same Chinese factory regardless of the brand stamped on them, Lyman, RCBS, Hornady, Midway, etc. so why pay more?
