I've used several of them from the SHV's to the NXS on AR's, varmint rifles and such. Never had a problem with them, but I don't flog on'em nearly as much as some here get to do.
I dig the shit out of the 12-42 Benchrest and the 15-55 Competition. The Benchrest is heavy, but the Competition is pretty much the standard in rimfire benchrest.