I've posted about my 9KT in a couple of places. Bought mine in October 2019, so not a first run, and a few problems were being reported on the model by then, but so had a lot of fixes. I bought mine with the intention of running it suppressed and having the PDW stock on it, as well as not shooting anything lighter than 124+P NATO loads as they were meant to do.
-I bought it on a Saturday, intending to SBR and run a can on it, this was mid October. RCM 80* lock piece wouldn't fit in the bolt. Emailed them, and Monday had an RMA printed out. Shipped it out to them on Tuesday, they got it Thursday. They wanted the gun in original condition and also wanted me to send the RCM LP in with it. So all of that went back.
-Repeatedly called and emailed, got zero information back for about two weeks.
-Finally got a reply saying the gunsmith had it and would check it out, expected to have problem resolved that week.
-Two weeks later again after multiple emails I am informed that the problem was "resolved" and that the RCM piece is out of spec and now fits, but this comes with a gap that is now .035 which is way out of spec. They suggest trying an HK piece or finding another locking piece that is in spec. In addition, they found a "problem" with the trunion but don't go into any additional detail and say the smith is recommending that they ship me a replacement. So I was getting an entirely new 9KT shipped back to me.
-Had to wait for the current production run (November of 2019) barrels to be treated so that they could send me the new one.
-I got my new 9KT back, and had to install rollers in it to get it to proper bolt gap with my LP. The LP had been stoned/lapped, and you could see where they had done it so that it would fit. Not sure what current production serial is, but mine was 002XXX, which was about Oct/Nov of 2019.
-Took the 9KT to the range, and ran about 1K of rounds through it. Zero problems. None. No FTF, FTE, nothing. I just shoot 124+P GDHP and ball, or 147 GDHP or ball and that's it. It has been reliable with the can on or off. No issues with extractor springs, ejectors, or the buffer; still using the original parts of all of those. No roller dents at all.
-I've never had issues with the sights, but I also added tritium front and rear sights. I tried an RMR but liked the irons too much and went back to just using those. Also put the MI MLOK hand guard on there with an A3 broom handle and Streamlight 3V light.
-I SBR'd it, which if I had any concerns or hesitations I would not have done so. I don't want to get into a $200 hole and be stuck with an stamped SBR that doesn't work. With the PDW stock on it for over the last 18 months, it has continued to be completely reliable.
-If you are going to shoot it suppressed, using heavy projos, and a stock then you need to replace the LP. If not, then you may not need to replace the LP to shoot suppressed so long as you are shooting lighter loads or not using a stock/brace. That varies by gun and from what I have seen reported you have to just try it to see if it will work. If you shoot suppressed without changing the LP, watch for tearing up your buffer or the start of roller dents or violent recoil. I have heard that PTR has been working to make their bolts closer to spec to accept the different LPs, but I don't have any personal knowledge of this.
-The knobs on the grip are slightly annoying, but not overly noticeable when you are actually holding it. They don't get in the way or anything, I would just prefer a straight/smooth grip. I do plan on switching it out for the Magpul grip module but it really has not been a priority.
-With the OEM backplate I didn't have any issues with the pushpins. With the PDW stock, the fit was worse, and that is universally reported on if you use the Choate stock. I expected it to be the case, and it was. It's not a huge deal, there is some wobble from the back plate of the PDW stock, but again that appears to be an issue with putting the Choate stocks on. Once the stock is shouldered and you snug it up, it doesn't wobble or anything during firing and it definitely does not interfere with or degrade accuracy.
-The front grip issues that I've seen have mainly been with the American production models, which seem to have a shorter ledge that fits into the recess in the trunnion. The HK (and maybe POF and other licensed builders) have a slightly longer ledge that engages the recess better. I have an American K grip that I used before I put the MI handguard on and it had a ledge that was long enough, so that wasn't an issue for me but I have seen people bring that up.
-As far as the magwell issue, mine is a little loose, but not problematic. Never heard of the issue being that the magwells were intentionally oversized for the crappy plastic mags. All my mags are the HK 30s and 15s, and they've all worked great and I have not had any issues with stripping/damaging the feed lips.
Regarding their other models, I have the GIR, the GI, and KP3 (set up as a G3K clone) models of their 91s. I have had absolutely no problems with any of those. I plan on getting another PTR shortly.