Yep, they are knock-off Magpul's or "clones" aimed at Airsoft so stay away if you can. Many of them do not fit your standard AR rails. I took the plunge once at a gunshow and bought a set of MBUS sights for $30 -- it proved too good to be true as it did NOT fit my AR rails. I'm not too upset because I'm only out $30 instead of $100.
The only ones that would really work are slings. I have 2 of the MS3 slings and they work just the same.