not so true Nightmarish as the gba is the best version as you can fix the music and colours with rom hacking, it is also in 3:2 rather than the super nes 8:7 aspect ratio which tends to work better on 16:9 screens, with that being said the picture is zoomed so you may or may not like that.
i actually completed FF6 on an android 5" phone when it came out on it, it was reallly nice to play FF6 without a horrible text font, but the battle interface was terrible, ff5 interface was perfect.
but yeah the interface will be really bad with a keyboard for ff6, i have ff5 android port on pc and it is literally just using the keyboard to move between actions which are designed for touch interface, it will be really really bad on the ff6 one, if they allowed mouse pointer on screen for battles it might be okay, you can even do that right now using an android emulator for pc and play it that way but there are some issues, mostly related to pressing the back button.