Product review (5 stars): This system prevents outside air (at present very cold) and ...
This system prevents outside air (at present very cold) and insects from entering the house.  It does not seem to restrict dryer air from exiting outside.  I believe it to be a clever idea that makes dryer vent well worth the cost of the unit.  In time the plastic exposed to weathering will become brittle (10 to 15 years) and break.  This is my second unit.  The first one lasted 18 years.