Something about MBA's is that with a Ph.D., even an MBA from a bad program might be useful. The thing about MBA's is that a lot is about branding and the branding element is less important than the education element for most people, whereas if you have a Ph.D., that's your brand.One thing about MBA's is that most good programs have a requirement of a minimum of a few years full-time work experience. I would hope that research done toward the PhD would count toward that, but I'm not sure.
It's like a dancing bear that speaks French. The fact that the bear speaks French at all is more interesting than how well the bear speaks. If you get a bottom tier no-name el-cheapo MBA, then you are a dancing bear that speaks French badly.
Also, I think that getting an MBA after you get a physics Ph.D. is a bad idea, and probably worse than a job working at Burger King. It's just less bad than getting a CS or MFE degree. One thing to remember is that school make money selling these sorts of degrees, and because they are selling them, there are some conflict of interests. If you go to a sports car dealer with cash wanting to buy a new expensive car, you can't expect the salesman to talk you out of it, because frankly that's not his job. So if you try to get information form a school about whether the degree is useful, or whether or not there are cheaper ways of getting what you want, you aren't going to get unbiased information.
There is a huge problem with "placebo degrees." For example, if you set your admission standards high enough, you won't have any problem finding jobs for graduates, but then you have to ask if the people that got jobs would have been able to get them without the extra degree, and in finance and physics Ph.D.'s, the answer is yes. If you pay $20K to a university and then get a job you would have gotten anyway, you boost up the employment statistics of the university, pay them money, and are much more useful to them than they are to you.
One other thing about MBA's. One curious statistic is that the US graduates about 1000 physics Ph.D.'s from all schools. Harvard MBA graduates about 900 people each year, and there are 100,000 MBA's produced each year.