Product review (5 stars): Keeps birds out.
I was having a problem with birds getting into the dryer vent. Installed this vent cover and the problem is no more. I suspect this also has a better seal then the standard horizontal trap door vent types. I used caulk around the base of the head as well to keep in place and to better seal it from outside air. There is also a small hole on top of the inside cup that I covered with caulk to make a good air seal. Now I do not have the back draft in my dryer when it is off.