MBL and German Physiks are the only omni radiator driver manufacturers that I know of also. Of course we have many variations on this theme. The hybrid of electrostatic and dynamic arranged in an omnidirectional sphere was the nearly forgoten Cosmostatic loudspeaker. Then you have the Quad ESL that emmulates the sphere using time delay of concentric rings. Or perhaps the Soundlab electrostatic that is mostly a planar but shaped as a portion of a cylinder. And then you have my beloved Shahinians which are multiple dynamic drivers arranged to emmulate the sphere. In my opinion, Richard Shahinians approach is the best to date. You get the omni sound with killer dynamics.