I used something similar for a couple years on my folding bike. I don't remember what it was called, but it was a similar design plus elastomers or something to dampen the bounce. I used thus because it raised my seat another couple inches, which was good. I didn't notice whether it improved the ride in any way until one day it became very bumpy. Thats when I realized the elastomers had cracked up and gone AWOL.

This thing may work for some riders, but it's a lot of money for a piece of steel wire.