* Is each transaction stored in its currency, or is everything converted to a main currency when stored? The latter is lossy and problematic.
* Does the app expect each currency to have a fixed exchange rate? If it does, that's problematic.
* You are asked to select a primary currency when signing up. Can you change the primary currency later? Will any information be lost if you do?
* How do you handle transfers from one bank account in one currency to another bank account in another currency? Will it handle an exchange rate that is different from the one the app might be expecting?
* How does budgeting work in multiple currencies, how are fluctuating exchange rates used?
I'll definitely be trying this out regardless of whether I get an answer here, I am really excited about the potential. :)