Product review (5 stars): Just like others have said don't reverse rotation or you'll unscrew ...
Inexpensive and did exactly what I wanted it to do.  Cleared out surprisingly large deposits in my dryer's vertical exhaust run, and went around two elbows in the process.

Used my cordless drill with the clutch set low enough that I had confidence I wasn't going to twist the plastic off.  Just like others have said don't reverse rotation or you'll unscrew it inside the duct and that'll be a real problem.

It's now sitting on a shelf, awaiting next year's annual cleanout task.