Product review (5 stars): Dryer Duct Cleaning Kit - Very Effective!  Should be used at least once a year for safety.
Dryer Duct Cleaning kit worked great, cleaned out more lint that I ever expected.  Dryer is now drying properly (was taking forever to dry before this).  One tip from another user: Run this from outside the house, then hook up a leaf blower inside the house and blow all the lint out.  Kept the laundry room clean, very effective at removing the now loosened lint.
Highly recommend, and should be done once a year to avoid fire danger of lint overheating in dryer duct.