Yes it works but not without modification - UTG MP5 Bidirectional Low Profile Clamp Mount

Wasnt interested in spending $$$ on a branded mount for my REAL HK91, not a clone. So I decided to take a chance knowing I may have to scrap this. I was already prepared to make some modifications so it fit properly over the rear diopter lips and was pleasantly surprised when it locked right on with no mod. I was smiling the entire way until I found once you lock down the claws they are not perfectly locked in level. For whatever reason that escapes me, the left and right side lips on the claw feet are machines differently. Seems like a flaw in the process because the left side of the mount has a nice 90degree lip that locks on the receiver tabs securely. The right side has a taper to each of the 'claws' where it grabs the receiver tabs. Because of this it doesn't really lock under the tabs but more compresses against it. So removing it and spending some time with a dremel (~ half an hour) to re-shape the lips on 2 of the 4 claws were required. Once I did this it locked on evenly and more positively. I hope leapers reads this and makes this change for the future productions. So many state this is junk and simply wont mount but that's not the case if you are willing to do some mods. Right out of the box there is something left to be desired. Yes I would recommend this but not unless you are willing to do some tweaks.
Pros: inexpensive
Cons: requires modification for proper fitment

This review was written in the old system and had content requirements that are different than reviews written today.