Product review (5 stars): Made in USA and works GREAT!
First off, I'm a sucker for American-made products, for quality and for keeping jobs here.  This fits the bill.

You need 2 things with a dryer vent closure:
- A good seal when not in use
- Easy to clean the lint

I've had this for about 2 years so I have an excellent idea how well this little gadget holds up.
If you don't know how it works, it's basically a 2-stage cover.  When you turn the dryer on, the air pushes against the inner cover and lifts up the outer cover.  When the dryer is done running, the covers settle back on to provide an air seal - good for not letting in the heat/cold in the summer/winter.

You can use this rain, snow, or shine, no worries about getting water into the dryer vent.

You have to clean it from lint every few months - just like you do with any cover.  Use a vacuum - the little crevice tool fits really well inside.

This little gadget does what it's supposed to do.  Works great.  A+