Had one, would never trade an AR10 (if I had one) for what I remember about my HK91.
AR is a much nicer platform with no weird brass muckups. The buddy I sold it to likes it fine.
Oh yeah, I really disliked the firing impulse, very harsh, and I am not recoil shy. Was a polygonal barrel, and that may have increased the jolt, but it was much worse than a M14.

HK 91
Dirty beast as well, all that blowback gas. Chamber almost as bad as an AR to clean properly, but with a lot more crap in it.
Bolt not so bad, bud you just have to dunk and swish to clean rollers, no taking it apart for thorough cleaning, at least the one I had.
Should have bought a MIA at the time they were even less $$ or about the same. Sure as hell was familiar with that rifle and the cleaning of it.