The iPad 2 Air is fine up to a point. I have the non SIM card version and it's nice using it because of the large screen. The problem is the weak to no GPS signal.
I use my Air when flying in open spaces and always maintain LOS. The problems begin if you hit RTH, for example; the Drone can't make its way to the takeoff point, it just descends wherever it happens to be at the time you hit RTH. In case of emergency that could be dangerous.
So for flying in a town or any suchlike, I use my iPhone 6.
That's my experience, if it's of use to anyone.