I used MS FS5 when I got my IFR endorsement, and was able to do it in the minimum hours needed, saving me at least a grand.
MS FS was the engine for some military sims in the early 2000's, and Qantas pilots did IFR currency practice on it when I was flying in NZ.
Although the terrain was pretty good, what made MS FS acceptable for pro use were the excellent instrument panels.