Product review (4 stars): Works as an extension to the Linteater kit
I already had another 12 ft. dryer duct cleaning kit (Linteater from a big box hardware store), but our dryer duct was over 20 ft. I bought this set as an extension to clean out the last 8-10 ft. of duct. You get six 2 ft. rods that have male and female threaded connections on opposite ends. The brush threads on the end of a rod and you thread on additional rods until you have the length you need. I inserted the end of the rod into the chuck of a cordless drill and used that to whirl the brush head.

Rather than thread all the rods to give me the total length I needed, I started with a single rod with the brush attached into the duct, whirled the rod back and forth along its length with the drill to pull down the accumulated lint. I used a shop vac to vacuum up the lint as I pulled down the rod. A couple of feet in, I then threaded on an additional rod and pushed it until it was time to attach another rod. Whirl back and forth, pull down/back to keep the lint from clogging up the duct and keep the vacuum running to suck up the lint. Keep repeating until you reach the end of the duct. If you try to push the lint further into the duct with the brush, you run the risk of clogging the duct with a big ball of lint that you can't get through (I know this from experience).