I own and have meticulously rebuilt and maintained three third gen Glock pistols: Two model G-21's, and one Model G-19 (RTF2). Between the three of them they have fired tens of thousands of rounds — all without so much as a single hiccup!
Well, that's not quite true; each of these Glock pistols has fired flawlessly AFTER I corrected the Glock factory's mechanical mistakes, and (mostly) 'for crap' incorrectly sized extractors, ejectors, and various other 'MIM' parts.
It took awhile; but, now that I've finally got all three of these Glocks up and running like 'a Swiss watch', and the BTF problems, and sporadic failures to return-to-battery are all finally things of the past, I've got to say that I really like my third generation Glock pistols!
In fact I far and away prefer each of these gen three Glocks to anything the factory has come out with since. I like the finger grooves, don't need gizmos like adjustable backstraps, or reversible magazine releases; and, in my own opinion, an enlarged magazine release head is just plain stupid. (I would know because I've kicked more than one fallen Glock magazine across the ground while moving fast with a Glock in hand! Experience has taught me that the smaller those inherently weak Glock magazine releases are, then, the better the magazines will be retained inside the pistol — where they belong!)
Here a personal suggestion for you: I've been working with and on Glock pistols, now, for more than 22 years. (I had no choice; I had to learn how to become an adept Glock armorer because, from time-to-time, the factory service out of Smyrna was so just plain drudging awful.) If you want a particularly trouble-free third generation Model G-19, I suggest you try to find a G-19 pistol that has a serial number that starts anywhere from 'A' to 'L'.
My own G-19 had a 'P' first letter serial number on it. The extractor was one of those early MIM junkers, and the ejector was two factory revisions too soon in order to work properly. Here's some more free advice for ya; please take it for what you will:
I would suggest replacing the 'captured' factory recoil spring with a Wolff Gunsprings, 'non-captured' guide rod, and a 17# Wolff spring assembly. (Yes, I know that 17#'s is one pound too light; however, Smyrna went to the current 18# spring weight in order to accomplish two things: First to, at least, mitigate the G-19's all-too-common BTF problems; and, second, to make the pistol more 'drop safe'. 17#'s is the original spring weight; and, if nothing else, it will give any G-19 a much sharper, cleaner trigger pull; and it will still be as 'drop safe' as any Glock ever can be. (No! Perfectly safe a Glock pistol will NEVER be!)
Here's a couple of pictures for you:
G-19(RTF2) Obverse
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G-19(RTF2) Reverse
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G-21 Obverse
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(The barrel is by Bar-Sto Precision. I have these barrels on all of my Glocks, now.)