First I heard of this, passing along the intel... http://booksbikesboomsticks.blogspot.com/2012/07/cheap-copy-of-what.html
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fyi magpul also has an airsoft product line that is much cheaper stuff.
I had some shmoe on gunbroker sell me Magpul PTS MBUS who was passing them off as authentic MBUS. He promptly returned my $ though for a return and stated "he had no idea".
MBUS PTS are supposed to have PTS on the sights themselves, but these ones didn't. They did come in the standard PTS cardboard box with that conveniently have no PTS markings. The sight posts are made out of the same weak polymer as the body of the sight is made out of while the real MBUS are a more sturdy and robust polymer with metal posts.