The way I see it is that the TDS is the real thing, it's geared towards real world pilots in it's operations, but within the sim it has limitations. While the PMS is geared towards the simmer.
By that I mean for ex. the PMS will give you extra functions it will give you the glide path, it will show you Traffic, it will show you the radar, it will show you the wind, you have simbrief and navigraph integration, the flight plan loaded will show up in the PMS, all "geared" towards the flight simulator for ex.
Both are strong products, just choose what you want.