Product review (4 stars): Pretty neat
This thing is actually kind of neat. If it's not clear, the cylinder has a removable cover and inside is a floating hat piece. When the dryer is on, the exhaust blows up the floating hat and air is directed down the bottom of the cylinder. I like how it directs the air down. My simple vent just went out and in the winter it seemed to contribute to ice build up on the roof.

When the dryer is off, the float falls and seals the port. Nothing can fall in like leaves or dirt and bugs are kept out since it only opens when the dryer is on. Also it should keep out drafts for the same reason. Cleaning should be pretty easy. Just remove the top cover, the floating piece and dig out lint.

This replaces a flapper style vent. When cleaning last time a couple of the flappers were brittle and broke off. I just removed the door and screwed this onto the side of the house. Took like 5 minutes.

One improvement might be some a foam gasket/weather stripping to seal it up. I have siding that angled and where the upper part attaches it's further out than the bottom. I screwed it on tight to get a good seal and almost cracked it. If there was foam it would be air tight around the duct and the duct itself. The manual suggests caulking the edges if needed, and I guess that's what I should have done.

Not sure if this will result in significant energy savings to justify vs a less expensive solution, but since I needed to buy something a good design seemed worth the extra money.