Product review (5 stars): Worth every penny, wish I bought it sooner
I am not one who usually does a review, but for this I had to.  This was quick and easy to use.  Our dryer was taking 2 and 3 cycles and still not thoroughly drying clothes.  There was air flow so I didn't think the vent was a problem.  As soon as I used this the lint was coming out in clumps.  I got to a certain point and I felt a little more resistance, nothing too much, and a huge clog came out.  The dryer is back in action as it was when it was new.  Worries about fires are also gone now.
I cleaned from the outside using a shop vac to blow through the duct.  Having done it once, next time I will pull the dryer out to check the first elbows, push it back and use it to blow through the duct.  The dryer blows harder than the shop vac.  Now that I have this I plan to do it once or twice a year.  It will take ten minutes and save a lot of gas and electricity with the dryer running shorter cycles.
We have a fairly long vent run so I also bought the 4 piece extension kit.  Using 7 three foot rods was no problem.