I have one, and it makes a good sound. The weight is not as severe as you might anticipate, and the mount method is reliable and seamless. I've only shot 45LC so far, but last night I loaded up some 460SW subs that I intend to try today; I'll report again once I shoot them.

So, if you want to discuss a silencer for your HK-91, post it in the HK rifle forum rather than the silencertalk forum. Telling someone they can't talk about silencers in a forum about their favourite gun brand is like telling someone they can't talk about a Ford muffler in a Ford forum.