When I bought my PTR-91FR several years ago, it was lightly used from my LGS and came with that mount, as well as some other accessories.
I can only speak for the one I own. (still have it if you really want one.)
To answer your question I have to compare it to the German mount which I now own attached to a Hensoldt ZF1. The key differences are this...
The German mount is milled, while the UTG is (I believe, not a metallurgy expert) a sand casted clone which is made in a mold, you can see the lines from it. Thus I wouldn’t put much faith in the actual durability of it.
When they copied it, the small rubberized piece that extends off the rear end of the mount helping to stabilize it against the notch meant for mounting a scope, slightly in front of the rear diopter sight, is just part of the molded metal... It doesn’t allow for the snug fit that the original mount offers.
The one I owned never held a zero for even an hour of shooting and was to me, an unmitigated disaster of a weapon part. I wouldn’t recommend it to anyone.
Pros: I got it as part of a very reasonably priced package, for you it’s a cheap option. It offers what the real STANAG does, which is a good view of the diopter sight for when your scope inevitably loses its zero.
On that note, I replaced it with an MFI low profile mount for a time which worked excellently, before buying the surplus Bundeswehr Hensoldt/Wetzler with STANAG mount I currently have on my 91.
If you have a scope already you are heart set on mounting to the gun, get an MFI, or I’ve heard good things about the B&T mounts. If you don’t own the scope already and want something that was made for, and works excellently on a 91, go with the Hendsoldt/Wetzler, it’s good glass, and they pop up at reasonable prices often. I couldn’t be happier with mine, and the mount works great. I realize this is a more expensive option but I assure you less headaches.