Do you want a 22 conversion for your glock? - Advantage Arms Glock Gen 5 .22 Long Rifle Conversion Kit w/10-Round Magazine

First the big question, do you want this instead of a stand alone 22 pistol? The short answer is no, you're goning to want a complete pistol. The advantage arms conversion kit with 2 mags is about 300, for 100 more you can get a decent Berreta, Ruger or Taurus 22 pistol.
But the advantage arms 22 conversion gives you something you will not get with a stand alone pistol: your own glock lower and trigger. The trigger control/ grip experience will be identical to your actual glock 19. This gives you valuable training experience you won't get with a 22 target pistol. Example: my Berreta 92/ 22 is definitely a better pistol than a converted glock, but the trigger pull is very short and feels nothing like my actual defensive sidearms. Meanwhile the advantage arms conversion is in every way identical to my actual glock except has no recoil since it's a 22.
The good: one of the best training tools you can get for your glock 19. You can double the number of shots you make at the range for not much more money. I'm paying 5 to 6 times more for 9mm than I am for 22 and that's getting worse not better. I routinely see 500 round boxes of 22 for about 8 cents a round and 9mm is actually starting to go back up with a "street price" of about 50 cents a round.
The bad: won't shoot cheap 22, especially during the 1st couple hundred round break in period. The worst Walmart ammo I can find will work ok in my stand alone 22, but won't cycle in the advantage arms. The company recommends high velocity ammo (1200 fps +) but you'll also find that some Walmart bulk packs labeled "high velocity" won't actually cycle the slide as they're purposely over estimating their speed for sales reasons and are more like 1000 fps.
I couldn't get federal cheap bulk packs to go thru the advantage arms until I had a bunch of much higher velocity Remington gold bullet through it to soften up the spring.
Another bad thing about the advantage arms conversion is the mags. Hard to load, more or less difficult to find (I had to back order a second mag when i bought the gun) and generally underwhelming. There are no 15 or 20 round models available so you're going to either have to buy a bunch of the 10 rounders or waste your range time loading magazines. You're definitely going to wish they had standard glock capacity 17 rounders for this when you shoot it.
Overall: one of the best things you can do to improve your defense performance is shoot a lot of ammo. Everything you "know" goes out the window in a panic situation and muscle memory takes over. So the advantage arms conversion is one of your best bets to maximize your training time with your glock, unless you have a boatload of 9mm laying around or aren't concerned with high ammo prices.