Product review (4 stars): Just what I wanted and Needed
My current vent opening was a an inviting door for the cold and mice.  The design of this product is simple and effective.  Keeps out the cold and the critters.  the only reason I knocked off a star was that most of the item is two pieces of plastic glued together.  The glue does not look very strong, the pieces are not perfectly aligned and there are a few tiny gaps in the glue.  I don't think that these slight flaws in manufacturing will affect anything short term or long term and maybe I am being picky.