All the info is stored either on the device itself or synced via Blockstack if you wish to do so. The project is also entirely open-source - https://github.com/lannister-capital
1) The app running on your phone is powered by the software on github.
2) This will not change.
The only way I would use an app like this would be if it were offered by a financial institution that holds my assets. If your app caused me to lose money, I would be SOL. If their's did, they would be required to answer for it.