The app is flawed by the fact that you start getting charged when the driver accepts the ride, not when you get in. This resulted in being consistently being charged DOUBLE the estimated fare. Why have an estimate if it is so far off?
The next huge flaw is that you need data to pay by credit card through the app. Confusing why this is the case... maybe to prevent fraud by the driver failing to end the ride but somehow every other ride sharing app has figured this out. If you DO have data then its not a big deal.
It is convenient only if there is no other option and you dont speak the language in a foreign country. It does have a scheduled pickup feature which is nice for airport rides, etc. Since Über was pretty spotty in Rome I used this but was annoyed every ride.