I've used the mercury reducers on my trap shotgun. They help some, but add weight to the butt of the gun.
They don't come close to reducing recoil like a muzzle brake. Put on a Sims pad, and Vais brake, and it will feel like a .243.
My gunsmith told me he noticed no difference in sound when he put a Vais on his .280. I put one on mine, and he was right. There might have been a slight increase in noise, but it wasn't noticeable to me shooting the gun. I'm sure it was for anybody standing next to me.
Any other brand of brake will be much louder.