Product review (5 stars): Did the job, superbly
Quick summary: I wasn't sure I could do the job as well as a professional service, but I took a chance and ordered this.  I finished the job a few minutes ago and I am very happy with the results.  I got about half a shop-vac full of lint out of my duct.  The rods are flexible but not flimsy, so they could easily work through the bends in the ductwork, but at the same time, could transfer the torque from my cordless drill to the brush head.  The ferrules on the rod ends were solidly made, so there were no issues with the rod connections, and the brush was just the right stiffness - stiff enough to clean the lint off the surface of the duct, yet soft enough to not damage flexible ductwork (the foil kind used for connecting to the dryer).  Just the vacuum fitting alone, without  even using the brush got out 80% or more of the lint.  It came out in huge clumps, so huge, it clogged my shop-vac's hose several times.  After I cleared the huge clumps, I used the brush from both the inside and outside (my dryer duct is around 20ft total).  The rods are sufficiently well-made that I think you could get away without any duct tape at the joints, as long as you're careful.

When I checked at the big-box home improvement store, you'll pay $40 for a similar product that includes just the rods and brush - and I'm not sure of the quality and properties of those rods.  This kit costs less, and includes the very useful vacuum fittings, plus a dryer brush (which I haven't used yet) and the clog remover.