As I heard it John.....the SFENA or SFIM as you will, was originally designed for the Mirage or some sort of fixed wing. It did have an altitude hold feature...which neither of the other two systems did. My recollection of the useless piece of kit was the unpleasant thrill one got when engaging the altitude hold mode.....at some point the aircraft either tried to pitch up and over onto its back or nose over and stick the nose into the dirt....which in a Bell can sometimes become very interesting. I dare say the quality of greenie support in Nigeria did add to the situation as did the lack of spare parts. I usually just left the SFENA in the "OFF" mode....and hand wrestled the bird. At least my blood pressure and heart rate remained somewhat more regular that way.