Product review (2 stars): Cheap Materials and Construction
Plastic construction is too cheap to be effective and durable.  After the first 2 months of use, the plastic lever wouldn't catch to keep the valve closed.  A small accumulation of lint hindered the moving parts from achieving their full range of motion.  I removed it after 3 months and threw it away.

The seams were loose and allowed a lot of air to escape.  Some HVAC tape helped seal it up, but couldn't overcome the fact that this is an $11 piece of hardware.

The concept is great.  Build it to greater tolerances and improve durability, and I'd pay $50 for the ability to switch between external and internal drier vent exhaust!