I know what a flash suppressor is, if that's literally what you're referring to, but I've never seen a claim that they reduce perceived muzzle blast.
A flash suppressor isn't going to help the noise of a gunshot indoors. Outdoors, maybe, but not indoors. Even outdoors, I find that claim dubious.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.