Being on a plane isn't technically dead time, but no matter what, it's still much more comfortable being on the ground.

And taking 6 hours total out of your flying time means you have 6 more hours to enjoy your destination. Unless I was a celebrity that would get hounded by the public, I'd rather do TSA Pre-check + first class supersonic than a private jet.

The caveat for me is that I wouldn't trust a startup that is behind its timelines to create a safe aircraft without further information.