I'm with mad_jock on this one. The choice is between a piece of dedicated software, written by a CAA flight examiner with more degrees than most of us have A-levels, specifically designed to train people to pass the IR skill test, and a computer game. Don't get me wrong, it's a pretty good computer game but, when all's said and done, it's just a game.
There will be those that sing the praises of MSFS as a training tool but they will tend to be those who are trying to justify their own decisions and not those who have been IR instructors, TREs or Line Captains.