X-Crafts has some very sophisticated modeling but till now no FMS SPD or HOLD functionalities available (i.e. missing some FMA modes), they've internally tested FMS SPD for long time but not released yet. FPS has some better systems, but LNAV is still bugging and VC modeling is quite not good.
So if u are going to fly on vatsim or airports mainly use RNP(-AR) approaches I would like to recommend to wait further.