Product review (5 stars): a good investment
The exhaust duct for my dryer is almost 30 horizontal feet, I've never been able to clean it. I needed to replace my dryer recently and purchased this tool so I could do the cleaning as well. It was surprisingly effective, reamed out years of compacted lint from the duct walls which the dryer blew though to the outside for collecting.

I did have to use my corded drill motor to drive it, the portable battery drill was too weak to force it though the turns in the duct. I started at the duct outlet end and worked it all the way in. Then I went inside to the dryer end and pushed it through from that direction to get full coverage. Airflow was very much improved, I expect to recover the cost in a year or two.