Product review (4 stars): a blow off solution....
the vent i tried to cover is very near the furnace unit so has an extreme amount of force... well, needless to say even with three layers of magnetic cover, it blew off big time.  so, i decided if the air flow was that strong, removing the vent and inserting the magnetic liner inside and replacing back onto wall with its screw should be genius.  WORKS... that air keeps it on like no bodys biz.  Happy now... my room is no longer like a sauna while the rest of the house gets warmed up.