I got the chance to fire off a few rounds of CCI Quiet .22 LR yesterday. It's a 40 grain lead round nose bullet at 710 FPS. Last month I got 2 bricks of it from Midway.
From my daughter's Savage Rascal with a 16.25" barrel, it makes less noise than a high powered spring piston air rifle. Remington CBee loads are louder.
From my Beretta 71 pistol it's a lot louder and sounds like a gun. It did not have enough oomph to cycle the action. I'm looking forward to trying it in my Ruger 22/45 with suppressor. I'm hoping the can will add enough back pressure to allow the gun to cycle.
I didn't test for accuracy as we were in a friend's yard plinking.
If you can find some and you have a gun that shoots it well, the CCI Quiet should make a good load for discrete pest control or small game hunting.