I'm not sure just what all goes on there. The description reminds me of the drivetrain on da Vinci tandems. The claimed advantage of the system is captain and stoker can coast while the other is pedaling. However, one consequence is that the "front" is a half-size set of chainrings with 4 cogs on it instead of the normal two. So it's a fourple instead of a triple.
Drivetrain Info - da Vinci Designs