They look like twins. Both held primarily by undisclosed inside investor(s). Can't find any info on Argon S.A. (Probably Saudi or some other secretive group.) Argon is an inert gas, undetectable.
I have no problem with secret owners but it comes with the Bermudian domicile and poor financial reporting. No significant institutional ownership in either EXM or BHO. Obviously they won't take the risk of surprise selling by insiders who have nothing to lose.