Not to forget: 4th generation pistols have: extractor, ejector, trigger bar, and connector issues that don't exist in all, but, the most recent 3rd generation models.
The most recent G-19 extractors are MIM parts. These extractors tend to be slightly oversized, gall easily, and frequently stick or operate more sluggishly than the former investment cast extractors.
The new 4th generation trigger bars have longer and more sharply angled sear, 'kick plates'. While undoubtedly less likely to, 'stack' than the older trigger bars, these new kick plate designs add appreciable weight and drag to the overall trigger pull and do not work as smoothly with the usual connectors.
In order to compensate for this added drag, Glock has come out with a new, 'dot connector'. It is very close in appearance to a standard 4.5# connector only the angle isn't quite as steep.
Nobody really knows what the story is with Glock's new #30274 ejectors? Word over at GT is that the extractor slide cuts have not been made deep enough on many, 'P through S' prefixed pistols; and this new ejector is needed in order to compensate for the improper machining.
Me? I don't know. I have a recent, 'P series' G-19; it has the older #316 ejector; and it works just fine. Consequently I don't think the factory's blanket statement that all, 'P through S' prefixed G-19's need this new ejector is completely valid. I think it has more to do with when the pistol was made and who worked on it.
As for the new RSA's? Glock seems to have some sort of, 'musical chairs' game going with these things. Personally, I'd much rather have my older RSA's (All of which happen to be from Wolff Gunsprings) than be forced to take part in this peculiar game of, 'musical chairs' that Glock has been playing. I have to wonder: Wouldn't it have been, both, easier and more straightforward to have made these things right to begin with rather than just dumping a mess of defective RSA's on a bunch of unsuspecting new Glock buyers?
When it comes to these new reversible magazine releases? OK that's seems to be a good idea; however, I have to wonder who decided to, also, make these new magazine releases larger! Glock pistols have long had a problem with unexpectedly dropping their magazines when the release button was accidentally pushed.
In the 9 years that I've been running Glocks this has happened to me, at least, 3 times; and I've read reports from several other Glock shooters who've experienced the same problem.
I don't know what to say about the new adjustable backstraps? I'm, 'old school'. My generation was taught to pick up whatever gun and use it well; but, that's not the attitude among today's more, 'option-obsessed' and demanding pistol shooters.
Personally, I could care less about a pistol with adjustable backstraps. I continue to be a gunman who will just pick up a gun - any gun: yours, mine, the enemy's, whatever - and shoot it well. This is how I was initially trained; and this is how I continue to, 'drive' firearms, today. To my mind, Glock's adjustable new backstraps are no more than, 'tits on a bull'. A pistolero can either shoot, or he can't. An adjustable backstrap ain't going to make no difference, at all, in your next gunfight.
Your, 'mileage' may vary; other gunmen might disagree; but, that's the internet. Given a choice between an older 3rd generation Glock, and a new 4th generation pistol, I'd take the older 3rd generation Glock every time!