Product review (5 stars): Oh, yeah, this does the job!
We had a dryer vent with a VERY long run.  Clothes weren't getting dry, and the problem was that the exhaust tube had gotten clogged with lint.  Due to the extreme length, I also bought the extension pieces.
Went outside, attached it to my cordless drill, and went to town.  Every so often I'd have to stop and attach another extension.  The most effective way to clear the vent seems to be inserting the brush and then backing it out a bit.  That way you're not compacting any material in front of the brush.  Have the dryer turned on (at an unheated temperature) so that any material you loosen will get blown out.
Well, I was working away and getting a large amount of lint removed when I must have finally loosened the major blockage.  There was a HUGE cloud of lint that came flying out of the vent, covering me (and a surprising amount of the lawn and shrubbery.)  The local birds were thrilled; they had lots of soft raw material for their nests.
-- I recommend that you use a face mask to cover your nose and mouth so you don't end up breathing all that lint! --
The dryer now works perfectly again, and this DIY cost much less than hiring someone to do the job.