Product review (5 stars): Totally satisfied. Follow the instructions to the letter.
I was able to unclog a 35 years old smelly and moldy 4 in wide going into 3 in wide dryer exhaust snaky 20 feet long conduit. It was taking hours to dry the clothing instead of minutes before , now it is back to normal. I started by unplugging my dryer and aspirating with a shopvac towards the dryer (adaptor provided) while I was inserting the brush with screwable rods at the tip of a DeWalt handheld drill from the outside of my house: no lint in the  shop vac reservoir. Then I repeated the roto-brush operation in parallel to the shop vac aspirator still by the dryer using the bypass opening adaptor provided: BINGO I got 1 gallon of moldy lint. Photos attached with my 12 in foot for size comparison. I tried to outsmart the directions provided in the booklet and roto-brush long lengths of rods without screwing/unscrewing them one after another. Do not do that; I regretted it; the rods will tangle on each other/warp and get somewhat out of shape, although not irreversibly. Besides it is dangerous to you too. Rods still usable despite my temerity. Am probably ok dryer exhaust wise for another 35 years. Preventive vac-roto-brushing is probably better than waiting for problems. Will not have to redesign the 20 feet exhaust (sealed) ceiling path.