Product review (4 stars): Works fine
This vent works fine and I rate it pretty well for that.

However, the top cover assy that has 2 screws attaching it in the picture is lighter plastic and you may want to get 2 nylon washers to allow the screw to tighten on those to prevent cracking and promote proper seating of the screws.

The unit needs a spacer built if it is to be mounted on a shingled siding because it must be close to exactly vertical to work right. The top and bottom mounts are separate pieces of plastic so a flush mount surface is needed.

I believe this unit is very efficient and works much better than the previous 2 vents I put on which cost more and both had 2-3mm gaps allowing outside air to go right in.  Get a vent like this if you live somewhere cold because those other vents are not airtight like this one.

The overlap type of seal inside on the 'floating' portion of the unit should work much better than flapper style vents. I had a flapper style with a seal on it for which the seal fell off leaving the 2-3mm gap. The flapper warped on its own causing more gap issues allowing cold air right in.

I can check this by feeling in the bottom of the unit and it seats after the dryer is off every time. The floating internal flapper has no issue floating right up when the dryer is on.