Product review (5 stars): Pays for itself.  A well designed tool.
I've got a fairly short dryer vent run with only a couple 90 bends.  Regardless, it was still a consideration that the recent performance drop in my dryer was due to some build-up.

I purchased this kit based on the mostly positive reviews here.  I wasn't disappointed at all with my purchase.  My one concern was a review that stated the brush head they received had a plastic coupling.  I didn't find that the case with the unit I received.  All couplings were metal, and the primary duct brush even included a set screw to ensure it doesn't come loose.  Keep in mind that the flex shafts do not have such a safety mechanism, so be sure to run the power drill only in a clockwise direction as the instructions clearly state.

When cleaning my own duct, I ran the brush into the vent from the outside while using the vacuum adapter with my shop vac at the connection where my dryer would normally be located.  My ducting is all galvanized steel from end to end; no flex duct.  I would highly suggest that when using a two speed drill, speed 1 (low) should be plenty fast enough.  Follow the instructions and take your time.  From the beginning to end, the entire process, including running the brush inside the dryer and vacuuming, took less than 30 minutes.

It's hard to fault anything with this kit considering its price and the amount of money one can save over calling in a "pro" to do the same job.