With the sets it would be nice to see the items themselves with the kind of Info you see on the official site. It's not required but it is extra info some people could like to see and would be expected in a knowledge base.

The tabs themselves should be fine, maybe some text on the class icons, you can figure it out in a couple of seconds but it's not directly obvious which class is which unless you're already familiar with the icons and there is room to fit it in unlike the tab section. I also assumed Crusader would be where Wizard currently is as it's the sixth class, I see this is alphabetical but things in game and other resources don't list them in that order, they're usually listed in the order of the game, so Barb, DH, Monk, WD, Wiz and Crusader. It's not an important change but keeping close to the game makes a companion app better and knowledge in game should translate over to the app, if Crusader is last in game list then it should be assumed to be last in app.

With the difficulty info, if you press to switch between regular and side by side then back to regular again, pressing the back button on the device will take you back to side by side and then back to regular again and will basically scroll back through the two however many times you did it until you finally get to the menu, all other entries pressing back brings you to main menu, this is just a little inconsistency I noticed with using the app.

All in all it's a decent app so far, it's just a good idea to follow the way things are done in game too, different people will approach things differently so the alphabetical thing for example may make more sense for some but not others, while everyone will share the same knowledge of the way it is in game and can easily transition between the two applications, a companion app should feel like an extension of the game, not something separate.