Probably the big difference is, the Futaba operates in the visible wavelength vs. the FMA, which operates in the infrared. The Futaba is very sensitive to flying over water but as I understand you can put blue filters over the sensors to help with that problem. Also, because it operates in the visible spectrum it's more sensitive to weather changes during the day. It works best on a consistent overcast day or you end up doing a lot of calibrations. I heard a tid-bit that the FMA sensors were developed in Russia and probably because they had infrared photo-diodes before we did. The US got behind as Russia continue to trade with China which is the only place to obtain certain rare-earth minerals and crystals

Phil