Not “30% fuel efficiency”, but an improvement of 30%.

FTA: “The project aims to demonstrate up to 30% improved fuel efficiency for a typical 250-nautical-mile regional turboprop mission”

I think there are startups making a similar sort of engine for general aviation. It's good to see that there is development of the same idea for commercial aviation.

This isn't like a hybrid car. It's a parallel hybrid, where the gas engine is just big enough for efficient cruise at altitude, and the electric motor/generator provides extra power for takeoff and ascent (or go-around power), and then charges slowly during cruise if needed.

This means that the battery is quite small and light, having only enough charge to take off and get to altitude.

I suspect that this system probably improves safety as well, if architected properly. If one or both of the gas engines fail, so long as they are not seized, that electric motor can still provide some power for diversion.