Alternative: get a tablet for the same job. If your camera is new enough to have wifi, it's a breeze to download jpgs; if not, Eyefi Mobi cards do the same trick.
Newer iPad minis--64-128g--hold many many images, display them at roughly 5x7--where you can really see what a effect a crop will have via 2-finger zooming.
Get the free Lightroom app, too, for far better editing editing on the go than you can get from the Aviary editor bundled with iPhone-specific photo posting apps like InstaFit. (The original specs of Instagram were awfully confining--everything cropped square, toy-cam "filters," ick.
If you already have a smartphone, great. I don't have/don't want one for other reasons. But with a 128g iPad I can do most of what I need a computer for, photographically, combined with the A7's wifi and Eyefi cards in my GR and Fuji XE.