Product review (4 stars): It was easily untangled though and was no worse for the wear
Cleaned 20 feet of duct from both ends with this brush on the end of a cordless drill.  Duct hadn't been cleaned for 25 years.  This brush pulled about 10 gallons of lint from the duct.  Make sure you follow the instructions when using the brush.  I had no problem when taking it slow and only running the brush in and out 1 foot at a time.  But when I tried to push the brush through a blockage it spun around on itself and got tangled up in the duct.  It was easily untangled though and was no worse for the wear.  Worked great and helped my dryer run more efficiently as well as removing a fire hazard from my home.  Just take your time when using it and don't rush.