Product review (4 stars): Good, but leaks a bit
This product does what it says, conserving heat and humidity inside the house during the winter and exhausting the same during the summer.  It was easy to install with the included clamps, and after two years of use I haven't had issues with lint dust.

I noticed that although the "summer" setting seems to be tight, a significant amount of the air escapes past the valve on the "winter" setting.  I would guess that about a fourth of the air escapes to the exterior in winter.  This means that I don't see 25% of the savings I had hoped for.  To look on the bright side, I am still saving 75% of the warm, humid air, so I would buy this product again.  However, I would prefer a product of better quality, even if it cost more.