Compared to any sort of side or top ported muzzle brake, they are whisper quiet and will make a huge difference.
Compared to a bare muzzle or normal flash hider, the difference for me is pretty subtle. I have several Kaw Valleys, a Hera, a V7 Helios...probably some others I'm forgetting. Not sure I noticed a huge difference between any of them, and not sure I noticed a huge difference (sound wise) from a flash hider or bare muzzle.
I think I have the Hera on my 18" because I convinced myself I could hear a difference at the range, and I have a Kaw Valley on a 10.4" PS90...again because maybe I convinced myself?
I also shoot suppressed on just about everything anymore so that sort of sets the bar at a different place.
