On light rifles say in the 375, 458, 378wby range they can reduce recoil by quite a bit. I have a friend who has one on a 338-378 wby and it's tamed that bad boy down.. BUT, you can feel the shock from it now standing ten feet away and you better wear some hearing protection. Your guide on a big game hunt will not like you either.. lol
some can be put on for practicing and taken off while hunting...