Product review (3 stars): Fan is wired backwards
I think this unit gives improved air flow, I just can't really tell.  Before installing unit, it tells you to clean the vent line, mine was 23 feet long and half plugged.  So after cleaning it, it obviously has better flow, I am just not sure the fan is doing a lot.  Two issues I did have.  One, I called the service guy and he was not very friendly and did not ask enough questions to get accurate information to give proper advice, then he was short tempered with me.  I am a Electrical controls engineer and work with factory tech people every day on the phone so I am a good judge on good service.  The second issue I have with the unit is how it is wired.  I took one of the reviewers advice and added a 120VAC LED and mounted it just behind the dryer to have a visual that the fan is running when the dryer is (I located the fan just below the floor behind the dryer).  Anyway, when i went to hook up the LED, i was surprised to find the fan is wired backwards of what it should be.  The Hot wire should go through the pressure switch so when the unit is off, there is no power to the motor.  It is kind of a safety issue.  Of course there is a ground wire connected to the case, but it is always a good practice to switch the hot and not the neutral wire.  This unit switches the neutral and has power in the motor at all times.  If the motor has a grounding issue and the ground isn't good to the fan, the unit will be HOT (120vac) all the time versus only hot when it would run if it would still run.