I certainly do like the idea of running the drive through the derailleur and gears. I'll bet it's a great way to save battery power and share the load without becoming exhausted.
It looks like an idea with real potential.
Though I was impressed with the idea and engineering involved in doing the same thing with an IC engine, I've not regarded it as being particularly desirable or useful. (Though I don't mean to knock SBPs product. I'm impressed with what they do.) But in an electric application, where conserving power is much more necessary, this looks like a real range extender.
I'll be watching with interest.