I signed up for the WingX free subscription for CFI's... I never got it, and stopped trying. I have yet to ever have a student using it. I do know of another CFI that has it loaded, but he has others loaded that he uses.
VFR guys will use whatever gives them a sectional, but mainly Garmin (especially the ones that work there) or Foreflight (everyone else with an IPad)....
IFR I haven't seen anything except Garmin and Foreflight, and again a heavy tilt of Garmin if they are employed there or running Android.
Either does what I need it to, I use foreflight. And I agree, it is getting expensive.