Product review (5 stars): This product was extremely effective
My dryer duct is about 25 feet long, so I actually needed two of these to fully plumb it out, but this did a great job for me. I went a couple of feet at a time and hooked it up to a handheld drill to make the brushing easier. The rods were flexible enough to fit around a couple of bends (and also to fold up in the relatively cramped space I had to work from).

My only word of caution would be to get a brush that's long enough to run the full length of your duct and work from the inside out; trying to work toward the middle from each end is not a good idea because it can create a blockage in the middle.  Relatedly, I did run into a couple of very large blockages in the duct where I initially couldn't get through.  They were about 12 feet from the opening and under my living room floor, so at first I couldn't tell whether there was a bend that I couldn't get around or just a bad blockage. I took the brush off the end and just poked the rods in to see if they could get through--they did, so I at least knew that the duct was passable, even if the four-inch brush couldn't make it through. Because I had two of these kits, I had two brushes, so I trimmed one of the brushes down to a smaller size and was able to fit it through the jam and open it up.  I then put the larger brush back on and cleaned it out.

Anyway, this really did the trick. A+ would recommend