What Number26 is doing is essentially: create a simple UI for accessing your bank account. Think of it as wrapping the "traditional" mywirecard service (= prepaid CC service with a terrible UI) in a modern interface with some added functionality similar to what your bank would expose via HBCI (which is usually offered by banks in Germany as part of their online account management product).

They haven't solved how to deposit money: you need to manually wire that from your real bank account into the bank account associated with your "prepaid bank account" for the MasterCard.

All in all, I don't really see the added value over my regular bank's web interface + PayPal (or similar). That's coming from someone who's got access to regular credit cards of course. And I - arguably - don't need real-time access to my transactions if I know that they usually show up on my online CC bill within 3 days max.