Just got a brick of CCI Quiet .22LR ammunition and tried a little out in the backyard today. Just informal shooting, only a few rounds but I think it is plenty accurate and also plenty quiet.
This is 5 rounds at 25 yards standing and leaning against the doorframe. I pulled the 5th shot. Used my prettiest Brno #1 with a 44 Mag scope on it.
As far as sound goes, it is louder than a springer air rifle by a bit. I compared it to an older RWS 34 with no moderator on it and found the springer to be slightly quieter, though much of the sound of the air rifle is in the spring and piston noise. The 34 puts out about 13 fpe while the Quiet ammo puts out closer to 45 fpe.
I don't have any other low velocity .22 ammo to compare it to. I have tried Aguila Colibiri and while it was very quiet, it was horribly inaccurate at anything beyond 10 yards. I have however, shot an unmoderated PCP in .22 that put out about the same energy (40 fpe Career 707) and it brought the police over to my backyard. The CCI ammo most likely won't do that, at least not yet... It really is "perty darn quiet".
Bottom line is that it is plenty accurate in my Brno #1 for backyard pest control though at 45 fpe at the muzzle, having a safe backdrop is going to be essential. At that power, I wouldn't have any concern shooting varmints up to the size of a raccoon with it.