For reference obento to bento, adding an 'o' at the start, is a matter of formality.
bentō to bentou, is a matter of whether we use waapuro romanization or the macron which is used in the real world where they aren't constrained by ascii characters.
I agree because that is the widespread way to refer to the real world japanese object, which are already literally foreign for people.
However I do foresee in the future discussions about the ou in character tags