Product review (4 stars): Works as Advertised and Easy to Install
I had the same problem as many other reviewers for this product have reported: an unusually cold laundry room that was noticeably cooler than the hallway leading to it or the rest of the house, even though the laundry room has a heating/air conditioning duct. After installing better weatherstripping in the window and more insulation in the (unheated) space above the ceiling, the room was still cooler than it should have been.  Turned out the problem was the cheap metal dryer flap vent which was perpetually held cracked open by lint and other debris, allowing cold air to come in through the dryer and to radiate through the thin plastic hose.

I can report that this device significantly improved the situation. The room is noticeably warmer since I installed it. The design is clever - on the inside there is a plastic cap that is blown up when the dryer is turned on, but because it is contained within the plastic housing, it will always drop perfectly back into place, sealing the opening, once the dryer shuts off. Moreover, there is no way lint can get caught in the wrong place to cause the cap not to seat properly. Note that you cannot see this interior cap in the picture, but if you remove the saucer shaped lid on top of the unit (which you CAN see in the picture), the cap I'm talking about is there on the inside, fitting over the tube that forms the terminus of your dryer duct.

I can't comment on the situation of the person (one-star reviewer) dealing with a masonry wall, who needs to get an appropriately sized piece of PVC pipe to use as an extender. What I can say is that I was able to properly install my vent on an insulated fiberboard exterior wall sheathed with aluminum siding in about 15 minutes. The mounting plate easily slid into the space between the sheathing and the siding. I ended up using a handful of that black exterior putty, aka duct seal, available for a couple of bucks at any hardware store, to seal gaps in the siding. I suppose you could use plumbers putty or caulk in a pinch, but the key point here is that you need to make sure you seal gaps at the siding/mounting plate/sheathing interface with something durable to keep the area water (and air) tight.

I spray painted mine black before I installed it, but I kept paint away from the inside part of the vent, to include the cap and tube described above, to make sure nothing interferes with the ability of the cap to pop off and then reseat itself.

All in all - a very good, easy to install product that performs as advertised.