Product review (5 stars): exactly what I needed
People are crying about quality - it's a dryer vent.  I've also seen (an removed) a lot cheaper ones, like the ones at the big box stores.

It's a little clumsy but works great - exactly as described.  Has a little flap in the main flap to blow off extra pressure (like if the screen builds up lint).  Seal up the edges with silicon or duct sealant if you don't like the very minor leaks.  Flap moves and locks well, and plastic housing is sufficiently thick.

If you're worried about the influence of outside air use an outside vent like the Lambro or Heartland.  You're dryer is going to leak air either way unless you use something that closes off the outside completely.  The only difference is you'll notice it at this junction before you notice it at the dryer but the same thing happens regardless.  It's not this devices fault.