I have had brakes installed on two rifles, a .340 Wby. MKV and a Model 70 SE in .458 Win. The .458 was a good shooter before the brake and remained the same after.
The .340 did not shoot well with 250 gr. Nosler Partitions before the brake, but it did well with 250 gr. Hornady Interlocks and with lighter bullets. After the brake it does well with everything, including the 250 Nosler.
There are no guarantees, but my sample of 2 says that it probably won't hurt.
Personally, however, if I had it to do again, I would have left both rifles unbraked, because the brake didn't reduce the recoil of the .458 very much (although the blast is not too bad), and although the brake dramatically reduced the recoil of the .340, the muzzle blast is nasty.
