Product review (5 stars): Awesome tool.  Best used with rigid ducts.
I used this to clean my own dryer line as well as a friend's.  It is very easy to use, and it worked great.  I love the shop-vac adapter.  Eliminated any mess inside the house.  My vent line is longer than the tool will reach, but not twice as long, so running the tool from both ends covered the whole length easily.  It went around two 90-degree bends with no problem.

I also used the softer brush to clean my dryer's lint filter area.  Got a lot of crud out.

Other than the little bit of flex duct that goes from the wall to the dryer, my line is 100% rigid metal (which I strongly recommend).  A cheap, thin, flex pipe, especially an old one, would get shredded by this tool.

I would replace them anyway, since they hold onto lint like crazy compared to rigid pipe.