A supersonic ram jet (scramjet) requires a fuel with a very high flame speed, so the combustion doesn't take place after the fuel-air mixture has left the engine. Aviation fuel would be completely unsuitable, and only hydrogen gives acceptable results. The low density of gaseous hydrogen, the storage problems associated with cryogenic hydrogen and the creation of a hydrogen infrastructure would had created tremendous problems for the Concorde development.
A scramjet is like wing sweep: It is best avoided if possible, but necessary if you want to go really fast. For the scramjet the speed above which it makes sense is Mach 4 or 5, and Concorde was designed for Mach 2.
The Skreemr at the present time is only an advertisement idea, so comparisons are not really meaningful.
Nevertheless, the difference with the Concorde is the expected range of speeds: at Mach ~2 a scramjet can hardly work (the air would be too slow at the combustion location).
All jet engines work on the same principles: compress (and slow down) the mass of incoming air in the compressor stage, heat it up in the combustion stage, let it expand (and accelerate) in the turbine/nozzle side. If the compressor stage brings the air down below Mach 1, it is not a SCramjet anymore.