I'm a little biased, but here's what I posted in another thread...
I just got one of these to test for BullpupArmory.com. It is solid as a rock, with a set-screw to secure. I would suggest some lock-tite on the set-screws.
There is one set-screw for the lug on an AR (with room behind the lug), and a second set-screw for the SAR 18. I don't have many rounds through it with it attached, and if you're going to put something expensive on it: check it often (set-screw/locktite).
But I give it a thumbs up!