I love the Kadet kit that I have on one of my P07s. I probably shoot that gun better than a lot of others simply because I run a lot of .22lr through it and have just gotten a feel for the thing. I've taken it out to MCFG and put 100 rounds through it, then swapped slides with the .40 slide and ran a box of .40 just as well as I did the .22lr. It would be great if every gun had that option. I've been toying with the Advantage Arms kit for my G23.
I have a 22 conversion kit for a 1911. I bought it to save money and shoot more. But I never felt like it helped me that much. I just felt like I was shooting a big 22. Maybe I would have better luck with a Kadet kit.