Shooting rimfire is very useful for handgun practice--up to a point. IMHO, the biggest contributors to missing the target with a handgun are the issues associated with recoil. People don't like the recoil impulse, the noise, the flash of light, or they just get the yips about the suddenness of everything happening at once. Shooting rimfire is a great way to "calm down" and focus on trigger pull, grip, stance, etc., but once you go back to shooting centerfire, you're back to facing the thing that's been causing you problems--recoil.
The Glock 44 is not a good choice for a .22lr semi auto. Sure, you get a Glock that's the size of a G19, but that's it. The weight and balance of the two guns are completely different. Shooting the G44 won't make you any better with your G19 than shooting a "real" .22lr pistol would, but at least a real .22lr pistol will be useful in a Bullseye Match.
I have four .22lr handguns. I love shooting them, and they do have a purpose in helping me shoot better. I try to fire at least a magazine of .22 every time I go to the range. But, if you are looking for a "cheap substitute" to get centerfire bullets on target, you're heading in the wrong direction.
