I think that going for an MST after completing a JD would cause a potential employer to ask "WHY?" An MST is basically considered an LLM in Tax for non-attorney CPA's. So, if you are an attorney the first question an interviewer will ask is "why didn't you get an LLM?" You could explain it away in an interview (say it was an economic decision - MST was 1/2 the price of an LLM), but I still think it looks odd. If it's a problem of admissions and can't get into the LLM program you want, then I'd get an entry level job at a tax law firm, work for a year, then get the firm to pay for your MST. That way you are not out of pocket for a degree that potentially won't get you a good "first job" anyway.