Product review (5 stars): Reduced Drying Time From 210 minutes to 40 minutes
This is the symptoms our clothes dryer had prior to cleaning out the duct:  It was taking three drying cycles (210 minutes) to dry our clothes. The laundry room was warmer than normal. The air flow at the outside duct was minimal.

We have an inside laundry room and would guess the distance between the exhaust vent in the laundry room to the outside laundry room is 20 feet or so.

I followed the instructions and removed most of the lint. We turned on the dryer and the air flow was still minimal. There must have been a bend in the exhaust vent system where the brush could not reach. From the inside exhaust vent, I attached the black plastic vent hole cover and used the shop vac exhaust to blow air thru the air duct and a big piece of lint blew out the outside exhaust vent. After that, I could feel a lot of air flowing out of the exhaust vent.

Drying time was reduced from 210 minutes to 40 minutes.