Why an outfitter would want his customer to be rocked by a shot and unable to follow up is a mystery. I would either find a different outfitter OR buy him a set of electronic muffs. Yeah brakes are loud. Pretty sure that's why God made muffs and plugsBrakes work great. But they can be loud and some outfitters will not allow clients to use brakes. So when you have brake put on make sure its removable and comes with a thread protector.
I ran hunts for 15 yrs. Worst case scenario is a guy with a 30-378 without a brake. Knew he couldn't hit the broad side of a barn before he pulled it out.
Some guns currently in use have the recoil energy equal to being SHOT with a small handgun at close range. How can that be a good idea?
Buy a good brake and if someone gripes that it's too loud, take it off and make HIM shoot it for ya.