Everyone that has replied has made excellent and valid points.
I would like to add this: choose the 22 LR unit that most closely resembles the type of firearm you intend to get and/or the type of shooting you want to do. If you like revolvers, consider getting the Smith & Wesson Model 17,18,48 (the older blued without the full underlug - my personal favourite) or the Model 617 (stainless with the full underlug). These models are 99.9% similar to their bigger brethren, the .38/.357/.44 models. This will allow realistic training at fractions of the $$ cost. If you are considering getting a semi-auto, consider the CZ 75 Kadet conversion kit or the entire pistol as this is 99.9% similar to its bigger 9 mm brother. If you have a chance to get the Advantage Arms 22 LR for the Glock, you one of the lucky few and should seriously consider adding that to your collection whether you are a Glock fan or not. In regard to the 22LR models I mentioned, these models have full sized magazines which replicate the feel of its bigger calibre brethren, and in terms of the revolvers, you can get speed loaders too. This adds to the "realism" of the training with 22LR.
All said and done, the choice is yours and as I did, I looked at the type of shooting I do, and the type of firearm (pistol and revolver) and bought my collection accordingly. When the wallet was a little empty, it was nice to be able to blast off 500 rounds of 22LR... and when the wallet was heavy again, I transitioned to the bigger calibres seamlessly.
IMHO.
S&W Model 17, 48 & 66
Glock 17, 35 & 22 AA kit
CZ 75 22LR pistol
Rifles & Shotguns too