Many people old enough to have played with 35mm SLRS in the 1960s-1980s have seen this lens before: it’s an obvious copy of the Spiratone “Circo-Mirrotach 90-degree lens attachment” sold by Fred Spira at his marvelous old Spiratone store in New York City.
http://twitter.com/Moeskido Moeskido
I remember the Spiratone store in Flushing, Queens. It was the only place I knew to get heat-seal half-frame slide mounts to view my Star Trek film clips on a slide projector.