Product review (4 stars): Works well, but follow the directions
I was surprised when I used the brush how much lint was in the vent. The brush does a good job of holding onto the lint and pushing the clogs through. Though you have to push a little harder, the rods are flexible enough to work through bends/curves in the duct.

The 12' kit was not enough to go from one side of the duct to the other (I wish that they sold a 6' extension rather than just another 12'), and you want to avoid coming up short and creating a clog. You might want to play it safe and just get the extension kit from the start. Or, if one end of the duct is higher than the other (my outside vent is above my head, while the inside of the dryer duct is ground level), start from the high end and push through to let the lint fall down the last bit of the duct.

The directions encourage you to tape the rods together before placing them in the duct. Though the rods easily twist into each other, the connection is not tight enough to prevent them from coming apart if you accidentally turn counter-clockwise, so the duck tape is necessary. The brush works very well, and if the rods were longer and held together without duck tape, I'd give five stars. Even with needing some duck tape and maybe needed to purchase the extension kit, this brush is much cheaper than having someone clean the dryer duct for you and much cheaper than other home versions available online and in stores.