Product review (5 stars): Well designed, inexpensive and it works!
I installed one of these in a customers home; the only way to vent the dryer was straight up six feet and then through many elbows twist and turns, far from optimal. The booster  installs in the vent line, plugs into a 120 outlet, activates with a pressure switch that senses when the dryer is turned on and supercharges the exhaust.

A very well designed device and it works; the instructions were not really clear, but the customer service is. I called,they answered the phone and the guy who designed the booster told me what I needed to know, elapsed time about five minutes.