I haven't done extensive testing, and I think other comments suggest it is really an individual combination crap shoot, but with the a linear compensator I played with, the thread protector gave the best groups. I thought the idea of a linear comp, directing muzzle blast forward, made a lot of sense, from a noise standpoint. Probably not from a recoil reduction standpoint, but I thought I would try one. My tiny group shooting 6.8 SPC, opened up. Not horrible, but from sub-MOA groups to slightly over 1 MOA groups. So the thread protector went back on, and I moved the linear comp to a Home Defense rifle, where accuracy shifts of that degree didn't matter. I also played with it on a 223 rifle, that happened to have a 5/8x24 threaded muzzle, and had similar results. FWIW, my best shooting AR barrels, have no threaded barrel, and a target crown. I keep getting barrels threaded, just to use my suppressors, but it sure seems easier to get to itty bitty groups, without a muzzle device.
Squeeze