Oh, boy, here we go! This is going to be a LONG post while I sing the praises of the Glock, so sit back and enjoy. Glocks are my favorite service-type gun and the G21 is my favorite Glock. I have a 2nd Gen G21 that I have been carrying on duty since 1992.
I have over 30,000 rds through this particular G21. I have run it wet, dry, upside down, right side up, from awkward positions, what have you. Aside from some of my reloads that I did not size properly, I have NEVER had a malfunction with it. Several years ago, an idiot firearms instructor who just KNEW better than everyone else ended up chipping off the bottom 1/3 of the extractor by dropping an empty case into the chamber to simulate a malf, then letting the slide slam home on it. Despite missing a LARGE chunk of the extractor, the gun still ran great. In fact, I didn't find the chip till I cleaned it that night.
As for the lead bullet issue, over 3/4 of the rounds through my G21 were lead round nose bullets that I reloaded. In a low pressure/low velocity gun like a .45ACP, I don't think the lead issue is an issue at all. Just keep an eye on the barrel and, if it starts leading excessively, clean it. I think the most I've ever fired at one time was around 350 rds and the leading consisted of just some smears at the end of the chamber. I would NEVER try lead in a 9mm, 10mm, .40 or .357 Glock with the factory barrel. Too much pressure and velocity if the lead does start building up and this can lead to a blown-up gun. The .45 should be a non-issue, though. Of course, this assumes that you use lead bullets that aren't dead soft. I use locally made (Mastercast Bullets in Enon Valley, PA) hard cast lead round nose and have never had a bit of trouble out of them.
Glocks are dead simple to work on, too. IIRC, even counting the magazine parts, Glocks only have 37 parts. A Glock can be detail stripped in about 5 minutes with just a 1/8" punch or even a ballpoint pen. Parts are everywhere and everything except the frame can be ordered directly from Glock, unlike a lot of manufacturers nowadays, who restrict a lot of the fire control components.
Mags are (relatively) dirt cheap, too. Last I checked, full-cap, factory G21 mags were $25.00 each, a far cry from some autos whose mags run $35.00 and up. I've seen used Glock mags at places like CDNN Investments for $9.99. They should be LE trade in and most LE agencies really don't shoot that much, so these mags should have a LOT of life left in them. ONLY USE FACTORY MAGS!!!!! I've seen normally stone-cold reliable Glocks turned into malfing, balky beasts by using aftermarket mags.
Holsters and accessories are readily available and almost every retailer lists at least a few.
Because of the Tenefer finish, Glocks are perhaps the most rust resistant guns out there. I have carried mine in downpours, freezing cold weather then going inside which leads to condensation, been shooting in pouring rain and almost blizzard conditions, have sweated like a pig on mine in the summer and have NEVER seen ANY rust at all on my gun. I can't even say this about stainless guns. The Tenefer finish is a heat-treat process and is not the black finish on the slide, so even if the black finish wears off, the Tenefer finish is still protecting the gun.
One of the best Glock features is the short trigger reset. EMPTY THE GUN, pull the trigger, hold it in, cycle the slide and slowly let the trigger out. Should travel less than half it's travel and you will hear/feel a "click". All you have to do is pull the trigger from this point to fire the gun again, no need to let the trigger the rest of the way out. Once you get used to it, almost anyone can run the Glock pistols REAL FAST! The trigger is a little mushy, but once you get the hang of shooting from trigger reset, the trigger feels almost like a factory, mil-spec 1911 trigger, at least to me. Pretty light and pretty short which leads t better accuracy.
I have never tried one of the "Short Frame" variants, so I can't talk to them, but the G21 is a BIG gun! Make sure it fits your hand before buying. This and the extreme grip angle are really the only complaints most have against the Glock pistols. Even most of those who can't deal with the grip angle will readily admit that Glocks are, overall, one of the most reliable pistols around.
Well, I'll stop there. Sorry for the long post, I didn't intend for it to be quite that long. It's just that I LOVE Glocks and try to share the love every time I can. They are great guns and, if you have big enough hands and can adjust to the grip angle, the G21 will serve you very well.
Bub