I have a Schmidt Bender PMII on a 7mm Mag. At a gun show recently I purchased a "Schmidt-Bender Polarization Filter" which is supposed to allow you to see through reflected panes of glass. In talking to someone last week they told me it was for Military and Police sniper use only.

Is it illegal to own this thing if purchased second hand from a gun show?

My second question is why would something like this be restricted from public use?