Re: Can you clairfy
"Isn't that a bit inefficient? "
Undoubtedly. But in a prototype that doesn't matter one hoot, because you're focusing on getting other more important bits to either work (at all) or to deliver some previously unachieved efficiency.
Regenerative braking is possible in theory, in practice it will never happen, because the aircraft's drag is normally the only braking it ever needs other than on approach and landing, and the weight penalty of any additional energy recovery gear would more than counteract the tiny recovered amount of energy.
I think where this hybrid tech eventually find a home is in keeping larger unmanned craft airborne for longer, rather than manned aircraft.