All - Cannot speak to Garmin units, but, in PMDG’s plane (737) you get choice of the default Collins or the Boeing unit, the Collins is more “RL” to me based on pictures of real cockpits. The default FMS in the 787 and 747 are different with the last update for the 787. I do not like that plane, the 747 and I go back to when it was introduced into the Real World, and have flown on couple. It’s FMS in game is very close to PMDGs one. I am awaiting the QOTS 747 to be released. I am not sure what if any FMS will be included in the C-17 from DC Designs later this year. I know it has one, not sure which one. Virtavia’s FSX did not have FMS in it’s release and its companion one in XP-11 was an older version of the FMS common in all the Big Iron Boeing Planes in that version. I tried to bring it over to 12 with many errors in plane. XP-12 uses an older FMS in all the Boeing planes last I flew one. Two updates since last used them, so it may have been upgraded and I am unaware.
PMDG’s tutorial for first flight in their manual is excellent, and several excellent FMS videos out on YouTube I have watched to get it figured out. New/current Boeing planes in RL have the FMS/AP/Flight Controls tied into each other to huge degree, so basically you make changes in the FMS and the plane does the revised stuff. I hate a computer telling me what to do.