I bought the Advantage Arms .22 LR kit for my Glock 21 and did some shooting with it against my CZ PCR with the Kadet Kit installed. The Advantage Arms kit is high quality piece of craftsmanship easily installed and going for about $239.00. The Kadet Kit goes for twice that and the quality is, well, CZ which means superb. First off the Advantage kit was not broken in, only 70 rounds, no mal-functions, with Mini-Mags. The G21 kit has combat type sights, the Kadet, target. I'm used to the hefty feel of the .45, the Glock with the kit felt light as a feather to me. The CZ felt like a full blown 9MM. The top group is the G21 kit the bottom the CZ. I'm not blaming the Advantage Arms kit for the large group, I'm sure that it was me not being used to the gun. I am well pleased with both kits. 10 Shots at 45 feet.