Certainly a unique sight but for all that went into it does it do much more than the simpler Rice sight? It appears to attach at the same point - the extractor bolt hole or rivet hole on later models - but requires the hockey stick-like projections on each side to keep it in line with the bore and two screws to each side just to keep the sticks in place.  The Rice sight is one piece and uses the windage "ears" for the dual purpose of windage adjustment and to maintain sight alignment. The Rice sight looks to have greater windage adjustment but the Mystery sight appears to have the advantage of dialing in repeatable elevation settings.  Being one-of-a-kind the Mystery sight is the better conversation piece but in my opinion the Rice sight is the more ingenious design of the two.

Close up of a Rice sight from an older thread that screws into the extractor bolt hole and the one on my sporter that uses a bolt and nut to replace the rivet (bolt and nut are not original to this sight).

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