This is just my opinion, so take it for what it's worth.
For years, I was pining on this gun, waiting for it to come on sale or even be available. I love Ruger to the point I even directly own stock in the company.
I thought it was a pretty innovative product, coming apart in two pieces. More compelling than the TNW ASR, which to me was meh...
After having the PC Carbine for a while, I noticed a few things which I don't like. And to clarify, I have the MLOK aluminum handguard version with the extendible stock.
1. I absolutely hate the take down and clean mechanics. It needs tools but not just that, Ruger recommends a certain Torque pressure in tightening. 65-inch pounds on the two main bolts - yes that's in the manual. My FAT wrench is on its max torque to the point where I will be stripping those bolts soon...as a result I don't use the PC Carbine anymore because I don't want to clean it anymore. Sure I can ignore the 65-inch pounds recommendation and torque it less.
2. Flimsy internal parts. In particular the shock buffer and the c-clip. Plastic fantastic. I swear I was going to break it each time. MCarbo makes a replacement kit for the shock buffer and c-clip which are metal. Think it's like $30 or so. That clearly is as a result of demand for a better mouse trap. Those kits get sold out often.
3. The weight ergonomics and distribution are off. I find it front heavy. Again, the MLOK aluminum handguard version. I have held the non aluminum handguard version and it's much better.
4. I wish I kept the Ruger magazine - I have the Ruger magwell but I traded the Ruger Magazine for a Magpul Glock one. It's a trade I wish I never made, in retrospect, even based on the very imbalanced value. I still have the Ruger magwell. Reason why I mention all this is because for my gun anyways, there are issues with the last round bolt hold open with the Glock magwell and Glock mags (doesn't matter if it's OEM Glock G4/G5, or Promag, or Magpul.
5. Accuracy is nothing to write home about. My new FPC has amazing accuracy and makes the Ruger PC carbine's performance look like an SKS.
6. I don't care about looks but the PC Carbine just looks like a plain jane. Nothing wrong with that, of course, but I enjoy guns that have a degree of innovative uniqueness. The PC Carbine is by no means a bad gun, but it's not the cat's meow that I once envisioned it was. That could also be my own personal tastes changing over time, but the aspects I noted above do contribute to my overall impressions on the gun.
Since I got the PC Carbine I got the FX9 (which is the easiest and fastest takedown of any PCC I own) and my most recent Smith & Wesson FPC, which I just love, love, love. Will probably end up selling the PC Carbine since I found guns which I enjoy shooting better.