The directed concussion of a muzzle brake can cause shooters to develop a twitch, ending up with worse accuracy than before. Anyone adjacent will be shooting daggers out their eyes at you as well. Muffs + plugs isn't enough for me to tolerate being next door to a braked .223, let alone a 308.
308 initially left me with a mildly sore shoulder, but I've found it does not reoccur if I shoot even occaisionally. I think recoil combined with just holding the rifle up tweaks secondary shoulder muscles/ligaments that aren't used much by new shooters. Unless the gun has a steel buttplate, you shouldn't be experiencing any undue pain until you get up to 30-06 levels, but the American is a particularly light gun. I'd reccommend a butt pad for your shoulder, and a cheek rest to help improve your fit with the gun, before adding a brake (unless you really want one anyway--in which case do all three