Well I haven't tried this on the metro pcs version as I only have the cricket version of this phone but this seemed a really easy method for me you might check it out.
Easy root (No Computer Needed) for any ZTE Score
This also worked for me to root a Straight Talk Optimus Q usin the same apks and method posted above. So it seems to work fairly well. I've heard that it's been more difficult to root the score_m since they updated it and closed the back door so hopefully this can help