Product review (4 stars): Reasonably easy to use and solid
The kit is reasonably easy to use, and a heck of a lot cheaper than paying someone to do it.  It's also solid - there are no parts that I feel are likely to break easily.  Just *BE SURE* to only run your drill in a clockwise direction.  If you run it counter clockwise, the rods could unscrew from each other and leave you with a rod and brush stuck in your duct work.

What I can't comment on is whether you actually need these or not.  They do say dryer duct fires are the number one cause of house fires.  However, my ducts hadn't been cleaned in the 9 years since the home was built, and not only did this pull almost no lint out of the ducts, when I pulled things apart to look inside, there was almost no lint in them to pull out.  In fact, the only place I had any lint build-up was on the plastic bird-guard that snaps onto where the duct leaves the house (and that admittedly was quite nasty - so I suppose the big upshot of me cleaning my ducts was that I discovered I need to clean that periodically :p).  At some point I do still need to pull my dryer apart and clean it.

... Still, this isn't a bad precaution to take, and it doesn't take a lot of effort.  Ducts in older homes may be worse, and some dryers may not capture their lint as well.  Better safe than sorry, right?

5 stars for construction quality and ease of use.  4 stars overall since I don't know how much they're creating their own market by playing off of people's fears.