Product review (5 stars): Works so well we now dry on a lower temperature!
The install was very easy.  You will need to purchase an additional vent hose.  I poked a very small hole in the vent hose and easily pushed the probe through.  I secured the probe with duct tape to ensure it stayed in place and to keep air from escaping.  This unit comes on immediately when the dryer starts and turns off about 5 seconds after the dryer stops.  It has been so effective in moving air that our clothes were actually coming out wrinkled because they were drying too fast.  We now dry clothes on delicate (low) and our towels on normal (warm).  Great piece of equipment.  Pretty quiet.  I get a bit of a hum in my house from so much pressure going through the line.  Kind of like a low tone from a pipe organ :)

Be sure to buy a lint removal tool to clean out your ducts before you put this on your venting system.  Just because air is moving doesn't mean it is safe.  Dryer lint cakes on the inside of the vent particularly at 90 degree turns.  I bought this one (Gardus RLE202 LintEater 10-Piece Rotary Dryer Vent Cleaning System) and had great success with it.

I highly recommend this to anyone with a long dryer exhaust vent.  I wish I had this 15 years ago when I bought this house!