Product review (3 stars): It helps but not as much as I wish...
It's not as wide as I needed, so I covered up the remaining vent with something, but it does help get that hot air out into the room from under my couch!  I still think that there is a fair amount of air that isn't being redirected, but since the air IS being directed towards my feet, it helps when the floor is freezing (I have wood floors).  I did use tape to keep the two pieces connected where I wanted so that they wouldn't move.