[marcosdumay]

I haven't been following those, but the GP's question wasn't about any of the things you enumerated.

The big question is: have they demonstrate a loaded plane flying through a useful distance while keeping enough reserve energy for satisfying the safety requirements?

Their videos are very well produced explanations about everything but this. There's some stuff about a few changes that reduce the reserve requirements, but still, I couldn't find anything about range.