As a relative newb to AR10's/variants, until now I had no experience with brakes. Once I started digging into them, it became pretty apparent that GOOD muzzle brakes could make a large difference in recoil.
With lightening my GII up by about a pound (barrel recontour), obviously felt recoil is going to increase. Even before the barrel recontour, the recoil was significant IMO (worse than a buddies 30-06 IMO, partially due to no buttpad I'm guessing), enough that keeping the scope on target after the round was fired was impossible.
I ended up with the M4-72 brake, because at the time, that was being shown as the most effective available.
I can tell you that without doubt, the brake made a massive difference. I won't go so far as to say recoil is at 5.56 levels, but shooting 130gr up to 190gr ABLR's with fairly stout loads, the recoil is significantly less. I can't put my finger on an exact, but I would definitely agree with testing that I saw indicating ~50% less recoil.
Yes, concussion and sound are also up significantly, but I would say to anyone that doesn't run a brake, and has no reason not to, try one. Especially one of the ones seen in various tests to be very effective.