Product review (4 stars): Works and does two things....
Reasonable price, better what I could get at the local hardware store.  I got this because I hated the fact I was sending all the hot air outside in the middle of winter.  I put this in, and then take the screen cap off and place a bounce sheet over hole and replace the screen.  You'll want to do this to keep down lint, but it put a nice scent into the air as well since the screen is of the standard screen door type, and lint dust will go all over your room.  Use the bounce sheets as better filter.  The added benefit of this was the return of humidity back into the home, which to me is an additional benefit having forced air heating.  My laundry room which can be like a freezer is nice and toasty.