Product review (2 stars): Very cheap and poorly built product, beter off making something yourself
I like the idea but the product is designed poorly, you get what you pay for on this one.  Could be useful if you can modify it yourself so it doesn't leak and so it will fit into standard size dryer hoses better.

This is a VERY cheaply made product, the inlet and outlet are too small to properly fit to 4'' aluminum flex duct or rigid duct...it will leak around the connection.  You may be able to get it to fit into one of those cheap aluminum foil flex ducts if you crank on the hose clamp really hard, but it will probably still leak.  Forget about using the 2 included clamps, they are basically just nylon zip ties.  When the valve is closed to vent outside, a good amount of air will still leak through the plastic flapper and vent inside your home...this will dump extra heat and humidity into your home in the summer when you want it to vent 100% outdoors. No gaskets or sealing valves on this, just cheap plastic...save your money.

Home Depot and Lowes sell something similar. Theirs is just as cheap, however if you buy from a store you can at least return it easily without paying return shipping.