Unpredictable
You make a payment, and two days later you discover that it was not processed because it needs to be approved by you. But the app says that you cannot approve it. You need to log in via a PC to sort it out. If you are on holiday with no PC, bad luck, you cannot make payments. Other times it works - but you can never know how the app will behave with your next payment. Customer Service says that "Yes, there is this issue with the app, we cannot do anything."