I can't disagree enough with the statement that training with a .22 is a waste of time. I have never, repeat never, seen a beginning shooter start with a centerfire that did not end up with a pretty bad flinch. Myself included. Well I can remember putting my SECOND .44 mag round, ever, into a puddle about 10 feet in front of me
Why train bad habits from the start? Coaches work on fundamentals first in every other sport requiring the least bit of physical coordination. Firearms surely aren't the one single exception where that's important in this world.
Disagree that a Glock is the easiest thing to learn on. In fact, I think the are one of the more difficult things to learn to really shoot well. Easy to learn to handle, yes. Easy to pull the trigger fast on, yes. Easy to shoot and hit what you are aiming at? Not if it's very far away. The only guns that are harder to shoot have worse triggers, and / or are lighter. The ergonomics of a Glock are OK but not necessarily great, especially if you have one of the double-stack guns and small to medium hands.
Again, how a Glock is immune to the ordinary suggestions for training new shooters, I don't know. You don't start a beginning rifle shooter on a .300 Win Mag or a beginning skeet shooter on 3.5" 12ga loads, do you?
Suspect that the only reason that training new LEOs could be considered a 'success' in starting a new shooter with a centerfire is that their qualification targets really aren't terribly demanding, in the grand scheme of things. Shoot reasonably quickly at something reasonably close. But qualifying on that sort of paradigm does not make one a handgunner, either.
.22 and practice, practice, practice some more. In the end I think it will hardly matter what brand so find something used that fits the hand reasonably well. Sight picture and trigger control are fundamentals that translate to anything.
And then buy a lot of ammo.