Product review (5 stars): Works as advertised!
Very happy with this product.  I have a long dryer run (~28 feet) that had not been cleaned since I moved in a few years ago and I knew it was accumulating lint.  I purchased this product and got to work.  As others have noted, you need to be careful about how you attach the extensions.  Don't add then all at once and then try to fed the extension in.  I did one section at a time, fed it in, stopped the drill, disconnected the drill, added the next extension, reattached the drill.  Worked like a charm.  I also cleaned from both ends to make sure I got everything.  Take the time to do this since you'll be surprised how much lint there is.

A couple things to note.  Doing this will deplete a drill battery in no time.  I burned through 2 18v batteries cleaning my vent.  Maybe sure your batteries are fully charged before you start.