Probably noone since there's no importer in the US.
Oberton is especially well know in Germany.
I own several of their drivers and can tell you that what they offer is the high-end for PA drivers. I owned drivers from several other manufacturers (e.g. Eminence) and this is just a higher class.
I know that the Dutch Importer builds subwoofers with Oberton drivers, before he used Eminence but he told me that after a summer of "abuse" the Eminence drivers were mechanically wrecked.....the Oberton's didn't have that issue.
The Ibanez Club #951, Dutch Bassists Club #23, SJSS Club #101 - 2x10 with coaxial mid/high driver, Bugera BVP5500