Product review (4 stars): flimsy -- but It works
This vent deflector is overpriced and made of flimsy plastic but it does what it is designed to do.  I use it underneath a sofa and it does a good job of diverting the air from the floor vent underneath to the middle of the room.  The deflector is approximately 1 1/2 inches tall so it should fit easily under most sofas.