It's interesting that they chose a supercharger over a turbocharger for their setup; the conventional wisdom is that turbocharging is more efficient than supercharging since it derives its energy from exhaust gases, whereas a supercharger is usually hooked up to an engine by a belt so it's sapping power from the engine. In normal use cases a supercharger has the advantage of instant response (whereas the turbocharger needs time to spool up after you throttle up. Considering the focus here is on efficiency, I wonder if Mazda uses a supercharger because they can decouple it from the engine when there's not much load (most of the time), and the small efficiency penalty is offset by the lack of spool time and less backpressure compared to what you get with a turbo setup.