Product review (5 stars): Stays on wall vent covers well
This vent cover did exactly what I needed it to do -- cover a "close-less" vent at the top of the wall in a basement room that does not need heat/air.  I was worried that the cover would blow right off, but it has not blown off once, and I have had it on for two weeks.  What is nice about these covers is that you can trim them down to size, paint/wallpaper on them to blend in, and you can use the byproduct from your trimming for other magnetic needs.  I would buy these again.