Just installed one on a Oly pre-ban lower. ZM sells "pre-ban" and post-ban" versions of their kit. The difference is that the post-ban's folding stock is pinned open.
I got the 11.5" barreled version and welded on a 5" CAR flash suppressor (to keep the legal 16" barrel length)- just like Bushmaster does. I also bought their optional folding/collapsable stock.
Unfortunately, I haven't had a chance to fire it yet.