I had a .45 JRC for a few years, it had the heavier buffer so I think that would be a gen II, but didn't have the quick release buffer tube.
Mine had feeding issues the whole time I had it, and I did the spring mod and upgraded all my Glock mags to JRC springs which helped. But never ran 100%. When it misfed it brought the round up too high and jammed the bullet against the top edge of the chamber. I filed that down but it didn't stop.
Accuracy was great, but I got rid of mine, and while the modified Glock mags ran fine in my Glock pistol it was a lot of time & money.
I sold mine for a TNW ASR 10mm carbine. it's not as well built as the JRC but has never misfed with stock unmodified Glock mags, and accuracy is as good. A lot lighter & slimmer too. If we're talking 9mm, I'd build an AR first. I've never had any malfunctions with either my Colt SMG pattern 9mm AR or Glock mag lower.
For what a JRC goes for these days, I think a Scorpion Evo is a better deal, more accurate and they work. My braced Evo pistol is one of the most accurate PCCs I own. Lots of aftermarket too.