Be interesting to see a comprehensive test done on trimmers to see the pros and cons and accuracy standard of them all. I have a Forster, had it for 40 yrs , so probably biased, as it has done the job, and I am used to it, change always involves a learning curve and getting used to a new tool. Forster sells 2 base lengths on the base ( get the long one), plus a 50BMG base. Their collets can be a bit tricky in that inserting the case wrong, can result in a crooked mouth. Their 3way cutters are somewhat lmited to calibers, and are more expensive, and not as easily converted to other calibers, than say an RCBS 3way cutter. Henderson is supplying odd caliber Forster cutters on a custom basis.
I also have a Hornady lathe trimmer, can put the RCBS 3 way on it, I find the case lockup pesky to use at times, but, that's about it, it tends to rotate when it isn't convenient. Other than it would be nice if they combined the trimmer, concentricity and neck turn units all onto the one platform, the way Forster does.
Also have the Hornady Trim/prep ctr, I haven't figured out a way to stop the trimmer from creeping short on it, and setting it to length can be an interesting experience. Love the prep side of it though.
And then there is the RCBS powered Trimpro 2, not sure if I like it or not yet, takes a pile of space, has to be mounted to a board and the base plate in the shellholder scratches the case bases, "universal" shellholder is very tight on this one, haven't properly set it up or done any trimming with it yet, but have discovered the shellholder needs some adjustability to it. Not sure if I like the lever system or not either.
I went a bit overboard on getting the 21st Century lathe setup over the years, have the neck turn and trim setup, like it a lot, even though it is pretty damned pricy, it seems to work the way it is supposed to, pretty easy setup. I just have the drill drive version, does what it is supposed to do, and is very versatile. Would be nice if the neck turn head and the trim head were both the same unit, haven't tried swapping pcs between them yet, look like they will though, just the trim pilot and neck turn pilot adj has to be figured out, I think.