On some devices the live feed will choppy and broken up. The otg cable will help with that issue. But if you don’t experience any issues with the live feed then the otg is useless and just an extra step before you fly.
I don’t know the answer as I don’t live that close to an airport but I believe that no fly zones are integrated in the firmware of the spark but like I said I can’t say for sure.
Same here with iPhone 7 Plus. Otg is the only way to fly now with the recent update. Before I couldn’t notice any difference in the feed between WiFi and otg.