machinbird:
Never had one in any of my military steeds. Sounds like it is more trouble than it is worth if you have to ride herd on it all the time to make sure it is telling the truth.
If you knew what you were doing you "didn't have to ride herd" on it, at least not on an ILS approach. It wasn't required to be used at all except on an ILS approach, at least in my 727 days.