I use X-Plane regularly for IFR practice. It's pretty good for that, with all the Navaids etc installed and doing the right thing, and with the option to fail bits.
I can't land it off an ILS, though - I can get to decision height with the needles close to the right place, but there it ends. It seems to require quite different handling to the "real" thing for the landing bit.
For VFR, I would say it's a definite liability - it teaches you to fly "head-in" and is hopeless for the important bits (such as landing).
I've not tried the latest MS offerings, but when I tried the "demo" of X-Plane after some time using MSFS, it was a different world. MS came off the PC and hasn't been used since.