Product review (4 stars): Good for the price. It gets the job done but could be improved.
This is a comparison review. I have owned both the Deflect-o  and the Gardus LintEater. They are both great at cleaning out duct work. They both have 12' extensions. The individual Linteater extensions are longer, 3 ft instead of 2 ft. They are a bit more flexible because they are longer. Neither extension will go through a tight 90 degree bend. The Defect-o brush is thicker, stiffer and probably does a better job of loosing lint that has stuck to the wall of the duct. The LintEater brush is a more sophisticated design. The Linteater has a set screw to help hold the brush head to the extension.
How they work:
The Deflect-o brush turns, loosens lint and pushes it along ahead of the brush. If your duct is longer than 12 feet you may need to buy extra extensions to push lint out to the outside exhaust port. It is generally intended for use in the direction starting from the dryer and pushing lint to the outside.( If you work from outside and push lint into the dryer room be prepared to catch it in a garbage bag or clean it up.)  The Linteater works by pulling lint out rather than pushing lint forward. The Linteater can do this because it's bristles are arranged in a spiral around the shaft like the spiral of a metal wood screw. This spiral grabs lint at the head/top of the brush and forces it backward behind the brush head. This approach works well for starting at the external exhaust vent outside. Turn on the dryer, insert the brush and run the drill. As the brush goes into the duct, it loosens the lint, pushes it backward toward the exhaust and the dryer airflow blows it out the exhaust port. The Deflect-o doesn't work as well(it works somewhat) in this dryer-assisted-airflow mode because the brush head is blocking the duct, pushing lint against the airflow and generally getting in the way of the lint being blown out.