The PTRs are great rifles, have owned one for several years. Mine is the 16" carbine version. I would say as far as clones fo they are one of the best. It shares alot if not all of the same parts as the original hk91. I swapped the original flashider for the fsc, it does a fairly good job. The older versions are threaded same as the original 91 in metric think it was 15x1mm rh, however the new ones come in standard threads 5/8×24 to except a wider range of devices. The barrel mine has is a bull profile, heavier than the originals. I added a vortex strike fire red dot to mine, as well as the hk oem adjustable rear sight assembly. I only run the hk steel mags in mine, have a ton of them, and a few aluminums as well that are very cost effective as opposed to others on the market. Mine currently has the factory rail system with the add on rails at 9, 3 , and 6 o'clock with magpul covers. I hope to one day swap it o the carbine g3 plastic handguard to reduce weight and balance the rifle out better. I can say that the fluted chamber does leave an impression on the brass when you fire it through these style rifles, however it has not effected reloading them. Only thing I do not like which is not really needed just wish it had been designed with a bolt hold open feature like the 40 caliber variant of the mp 5 I had. Thats the only thing I can say I would change. I have the zenith mp5 in 9mm, the 91's little brother their is alot of similiar features in these rifles. I would say the ptr holds a 1 moa group at 100, and I have never had a malfunction with it. Its not picky about small base reloads that some of my ar's in 308 perfer. I can say I would recommend them, they have a high quality, and perform well, if this is the kinda rifle that your looking for.
Here is both of mine the 16" ptr in 308 and 9mm zenith. I owned a vector v5-40 or mp5 in 40 caliber, but a friend talked me out of it years back. Sometimes I miss it.