Concept in drawing looks like it came out of the 1950's
with large wings and verticals.
Maybe that's what flateric means, maybe this concept came
from Popular Science.
Would be interesting to look at what happens with those
at ~ M20 at the altitude they intend to travel at or go through.
I would expect lots of drag.
I'm fairly impressed with the Reaction Engines efforts in the UK.
They seem to be converging on actually developing the SABRE
concept, if rather slowly. They may be the ones to beat.