Product review (4 stars): Works pretty well
It works pretty well, the only problem I had while using it was when I encountered a 45 degree bend in my dryer duct.  The brush wouldn't go past that bend for some reason so I had to go up in my attic to take the duct apart at that bend and clean the rest of the duct from inside the attic.  Very inconvenient to do in the Florida summer where attic temps are probably approaching 130 degrees.  My duct is probably about 18' long in total.  I purchased the extension kit which I didn't end up needing because of the above.