Product review (4 stars): It works as advertised. Only longer term usage will ...
It works as advertised.  Only longer term usage will determine whether the air-flow flapper stays in the desired position *and* prevents air leakage around the perimeter, i.e. seals well enough that hot air during use doesn't come inside when in the bypass position, nor continues to the outside when directed to the indoors position, which is what happened to the previous one we had from a different manufacturer.