What I understand from directivity boils down to what is explained here.
In the video you see at 11:40 some info on directivity mismatch and how that mismatch gives you bad "in room"
This is the case for flat on axis FR speakers. But in this case the "in-room" is smooth...
That is what I try to understand from this design.
What problems you see this speaker has because of it poor directivity? They have wide dispersion and smooth in-room.
Again I think the approach they use is different and not what we used too and surely not textbook.