Anything that builds repetitions of doing it the right way is of value, to my way of thinking. .22 conversion unit, airguns, Airsoft, whatever...the closer in feel and trigger pull, the better. I really like the SIRT pistol as an understudy gun for Glock shooters; search under SIRT here at GT will turn up lots of good stuff.
Big difference I've found is that with light to non-existent recoil, it's real easy to get sloppy with weak grip or feeble stance, since recoil isn't there to remind you. Watch out for that, and you'll be building good reps.