I'm actually surprised they're relying on Activities for the views in the app. I'm not familiar with how the app works, but this is typically an out-dated approach. Activities should really only be treated as entry points into your app.

Also, not a huge deal for an app, but the package structure is organized by layers, not features. Makes Java's non-private access modifiers essentially useless.

The general style of the source code is solid though. I wouldn't be upset if I had to work in this code base on a daily basis.