I have a Gemtech Halo on my .223 4gery and IMHO it was worth every penny.
As an experienced handloader, I fire both full-power (3100 fps) and subsonic rounds.
I have developed subsonic rounds that are even quieter, but MORE DEADLY than a 22lr. 22lr is usually only packing 24~40 grain bullets. My subsonics are 60+ grains which would be closer in target energy tranfer to a 22 magnum.
A 22lr is actually a transonic bullet. It leaves the muzzle at supersonic speeds and then transitions to subsonic in about 30 yards. So even a silenced 22lr will have a sonic crack. That is also why 22 subsonic is MUCH more accuracte than 22lr. My subsonics leave the barrel around 50 fps. under the sound barrier and have a velocity deviation of only 15 fps.
My subsonics do not cycle the action but that makes them even quieter because you do not hear the gas pop from the BCG exhaust ports. It makes it a Repeater action and not a single shot. It is possible to make subsonics cycle the action by having your gas port drilled and installing an adjustable gas block. I choose not to do that because I love my subsonics & can just the way they are. The total sound is less than a daisy red rider BB gun. I can actually hear the hammer hit the firing pin.
I do quite a bit of nocturnal varmint killing around where I live. My varmint magazine consists of the first round being subsonic and the following being full-power. If I happen to miss with the subsonic, I rack it once more and blaze with full-power. I have never had to rack it yet.
Needless to say, I have (and am still having) an absolute blast with my Halo can.