Product review (5 stars): GREAT idea - well-executed
Total success.  I hate those metal louvered things, and big-surprise, they don't keep pests out of the house.  A neighbor's dryer had stopped working entirely a few years back, upon his return from an extended inlaw visit (part of the reason I bought this, as you'll soon know).  Due to his limited retirement income, I helped him pull the dryer out, and we poked around to see just what had the dryer belly-up.  Maybe we two knuckleheads could fix it by accident?  Anyway... Guess what will stop a clothes dryer?  Answer:  pecans - lots and lots of pecans

A mouse (we guess) started putting back pecans for the winter, and by remaining steadily at it for we estimate the entire couple of weeks he was away, managed to get enough pecans into this dryer to jam up the whole works!  I couldn't believe it, but true story.

Anyway, fast-forward to me getting this vent thing and using it.  It fits standard (4-in?) extension dryer pipe (solid kind, not flex/corrugated) that you would run through a wall, and sealed up perfectly just pushed in - you can seal further at your option, which I did.  Then, you pop 6 holes in the side of your house, run in some screws, and voila!  You have something I associate more closely to a "commercial-duty" vent solution than the old standard.

Everything that's true about occluding pests is just as good for cold air.  You don't stop it from being cold outside, but you stop cold air from pouring in through your dryer.  In the right weather and prevailing wind, I could keep beer cold in my dryer (when not in use), to say nothing of the energy wasted by chilling that whole end of the house.  This was probably far and away the largest inefficiency with my heating/cooling - you'll hear builders talk about 'the envelope'.  Well, mine had a large gap in it, through which I was throwing money each month.  Guaranteed, the first February alone, this paid for itself.  I've never felt even a puff of moving air come back through this thing.  It's still connected to the outside air, and not particularly insulated or anything, so it isn't magically warm ... but it's the air movement I wanted to stop, and that's what it did.  I'm trying to guess just which way the wind would have to blow and swirl to defeat this design.  My guess is, if that ever happens, you have bigger problems at that particular moment, considering shingles are held down on one end largely by gravity too...just sayin'.

This is particularly important the closer to the ground or more easily accessible your vent location is.  You cannot install this upside down or sideways though.  The inner cap floats up and allows air to escape when the dryer is pushing air, and when the dryer is off, the cap floats back down and seals perfectly by being 100% in line with gravity (in contrast to a flapper that is based more on 'leaning' closed, rather than 'falling' closed).  I say that to say this:  critters know how to nose and pry their way into things, but don't generally posess thumbs and all the finer motor skills and intellectual prowess to arrive at "YOU MUST lift both sides of the cap straight up at the same time, or it'll bind in the housing".  Truth be known, I've witnessed full many a human found wanting in that particular comprehension...  Anyway, forced air does that nicely ... mice, not so much.

BOILERPLATE:  It beats the standard vent cap/flapper (which my neighbor had intact on his older home), and I dig it.  It also doesn't rattle/flap in the wind, so it's the silent option.  I generally go for the cheapest thing first if possible, but this seemed to be, and later proved to be so superior that I don't miss the extra duckets.