Product review (4 stars): Necessary for some applications
Praise to Amazon because I could not find this product at the local home improvement stores.  I could find the type that make an S-shape, but limit the length to about 4', but not this type with the transition back to 4" duct.  This is perfect for my application:  not the typical application in that I want to put the dryer closer to the wall, but rather I want to get hard vent ducting behind some drainage pipes in my basement.  I previously had a section of slightly compressed flex ducting there that I wanted to get rid of because flex ducting is never the best and always develops holes over time.

It loses a star because of the loose tolerances where the three pieces connect to each other.  I used rivets and proper air-tight foil tape to keep it all together well.