Product review (2 stars): Air Blowing Out of Vent Caused it to Float Like a Ghost
Well, you get what you pay for, sometimes.  I was attempting to install it when the air conditioning came on, and it floated away.  I put a piece of broken plant ceramic I save for drainage in other plant pots, and I guess I'll eventually use some carpet tape to make it stay, but it will divert the air if you work at it. ha.  I just didn't see anything else that would work under a couch.  Furniture sits low, and those other vent divertors (sp) are too high.  Good luck!