Product review (4 stars): easy to install, keeps heat we paid inside the house !
This is basically a plastic box with a flap valve inside. Once I put a little super glue in the joints and pressed it together tightly, I liked its looks a little better. It has a rounded back, so it's not designed to mount on the wall: but I did anyway with a few drywall screws. The valve flap moves easily; also it has a mini-flap in the center of the vlave flap so that the dryer doesn't blow too hard into the house. The clamps that come with it aren't the best. I finally paid $2.50 each for hose clamps at the hardware store; these guys really hold tight !

I used to hate the feeling of seeing all that steamy air streaming out of the house; it was like watching dollars blowing away ! This item seems like a good fix for that problem. Future electric bills will tell.