Bring back some helpful advanced training for the iPhone!
There are two features that I personally love but which are now removed:
Only just removed - repeating a sentence spoken in Spanish without seeing it on the screen. I loved this one, helped me with my "listening" skills.
See a sentence in English, speak it in Spanish. This has only existed on the desktop version, not mobile. I'd love to see it on mobile too.
Basically, add more features for those of us who have finished our trees but want to keep using the app to learn more.