Product review (5 stars): Actually works!!
I removed probably about 2 gallons of caked on lint from my duct.  Had no problems using although I wasn't able to use the vacuum attachment as my shop vac's hose was too small.  Nonetheless, I sent the brush through about 10 feet of foil duct (once from each end) and then followed up with manually removing the the lint and then vacuuming the leftovers.