Twisted Industries now have a Keltec P11 conversion kit available. I am a fan.
.22 conversion kits have two main purposes: reducing ammunition costs to between 10% (with 10mm Auto and similar) and 20% (in 9mm), and also easing the wear on the hands. That reduction in fatigue becomes a real factor with subcompact autoloaders and small revolvers. With revolvers, centerfire and rimfire gun pairs serve the same purpose. While you can’t learn recoil management with these, trigger control and other basics work the same as with the centerfire slide.
With this Twisted Industries kit, the weight of the pistol is much reduced, giving it a secondary “kit gun” use. By providing billet aluminum magazines, TI pretty much makes them last forever. These are easy to load without any tools. The converted pistol and magazines fit the same holsters and mag pouches as the original. Since they are reliable and fun, I probably shot 25 rounds of .22 for every one in 9mm through my PF9 kit. Just got a threaded extended barrel for it, so will report on suppressed performance soon.