On their are better app like moovit to travel around paris, then I would strongly advise to get yourself a recharge STIF card to travel around Paris.
Very easy to use. Takes a few trips to figure out.
Very good helped me lot.
Helped with metro, not much else
Works ok for the train, does not work at all for the bus. Sometimes closes on its own leaving you without information while underground with no gps signal. Walking directions to stations are completely inaccurate, consistently. Cannot lookup the train stop as a location.
It's actually not a bad app if taking transit but I found Google maps better for walking directions. Best thing I can say is use what works for you.
In this new version of the app, we added the airport shuttle Go C Paris to join Pont de Rungis station (RER C) and Orly airport. Enjoy your visit in Paris !