Product review (5 stars): THUMBS UP!!!
It does exactly what it is supposed to do.  I use it to redirect the floor vent airflow under my china cabinet.  Some have claimed that the Extend-A-Vent is very fragile.  I have found it to be a fairly durable plastic.  It comes in two pieces.  It seems that for most applications, both pieces could remain stacked together as they are right out of the box (i.e., double thickness - see image).  This greatly adds to the durability, if that is an issue.  If one needs it longer, then purchase another and use the two together.  The material can easily be modified with scissors and/or glue (or tape) to fit custom needs.  By the way, if need be, small magnets (found at most hobby shops) can be added in for those with metal floor vents.  I highly recommend it.