Product review (2 stars): Deflects air but could be made much better
I purchased the Dundas Jafine EXTVENT Extend-A- Vent Air DEF to go under my couch.  This is made of extremely thin plastic.  It comes with one clip to attach it to the vent which i was not able to use.  The two pieces of this extender do not connect together with anything so I had to tape them together to keep from separating.  I think this extend-a-vent is extremely overpriced for the quality of the item.  It does serve its purpose and deflect the air.  You just need to add some tape and creativity to get it to work for you.