Product review (5 stars): I love it!
No more ice cold dryer in winter!  This device is ingenious.  Allows the dryer to vent properly, but seals out the elements, critters, and cold when the dryer is not in operation.  The only downside is the material it is made from.  I have lost one to age, as the hot/cold cycles seem to break down the plastic over time.  I lost another to a hail ball strike to the lid.  I wish there was a metal version that would outlast the dryer.  But they are easy to install/swap out.