I primarily use my phone for wide shots (landscapes, sunrises) and sometimes for macros.
The good/great:
1) It gets rid of that ring around the rising sun, at least mostly and much better than the native iPhone app.
2) Much better in high contrast situations (like sunrise).
3) Nothing is lost when importing to Lightroom and exporting from there, unlike the native app.
4) Takes excellent macro shots when it allows you to switch to macro mode - at least as good as the native app.
5) no need for additional hardware or extra lenses!
The challenges:
1) It's a litlte glitchy and it's frozen on me twice.
2) If you change a manual setting, such as exposure, but then you close the manual settings bar it goes fully into auto mode. I usually set my exposure to +1. In the native app, everything I take from then on is +1. In Project Indigo, this is only true if I leave hte manual controls open. If I hide them, it is no longer at +1. Where this gets a little awkward is that if you have the manual controls open, it won't give you the option to switch into macro mode and there is no way to manually switch. You have to close the manual controls, let it prompt you, switch to macro mode and then reopen the manual controls. It's no big deal really, but hopefully something they may fix in the future.