Product review (5 stars): Helps bring air into room if vent is obstructed.
These are nice to direct air flow if you have a couch or other large object that obstructs the vent cover.  My dog tends to hog it during the summer after playing outside.  Funny to watch her plant herself in front of it as she knows it's direct A/C.  That's proof that it works.

I secured mine with painters tapes all along the side and back to make sure air only comes out of the front. Very effective after that.