22 are great for low cost target practice. Remember that sight picture and trigger control are the two most basic fundamentals of marksmanship. I found that the humble 22 serves well in this regard.
For that reason, I bought a Colt Diamondback revolver, a Colt Ace conversion kit for the 1911 and a CZ-75 Kadet conversion kit. With the Colt, I can practice a lot of DA shooting. Now, if someone else pays for the .38/.357, I don't mind shooting 300-500 rounds in one session. It's a matter of what one can afford.
The semiautomatic conversion kits are wonderful to train on. You get the heft of the regular gun, trigger pull and function with virtually no recoil (except for the Colt Ace - thanks to Williams' floating chamber design).
The only problem is that no one makes a full size .22 pistol which is DA/SA like the Beretta 96, Sig P220 et al. About the closest I've come is the miniscule Beretta Bobcat .22 LR.
And for those of you who laugh, I've trained cops who were poor shooters with .22. When an agency is poor or cheap, it may be the only cost effective alternative before you break out that last case of 40 or 45.