That's just another 'spring tensioner'. The idea sounds good but the fact is you don't want a spring that allows slack when you least need it. The tensioner, if you have to use one should be mounted solid. Adjustable, but not by a spring.
When pedal starting or during deceleration the spring will give allowing the chain to loosen. You don't want that. These are a bandaid for improper chain tension and a marketing gimmick.