Its an interesting horn design, but of course it is essentially only one driver to be built into a full range speaker system. Like most things, the results would depend on how well the whole end package is executed and the only way to know if it were truly an upgrade in the end would be to try a system that uses it and compare. Assuming 98db efficiency and a flat response along the lines indicated by the chart showing measured response of the custom built design in the reference provided, those are a good set of initial indicators, but of course do not assure anything.
I'm assuming the multi-driver design of this horn helps achieve higher efficiency? Other than that, I am not sure what the advantage of horn loading 4 midrange drivers rather than one would be? I am not a fan in general of systems that use multiple drivers to cover the same part of the frequency spectrum because I believe it is harder to do that well and costs are driven up.
An interesting and somewhat different design nonetheless and one that has apparently been built into some affordable end user systems, so that is good.