Customer Bitcoin balances, according to the companys chief financial officer Christoph Iwaniez, are booked directly on the Blockchain via a multi-signature wallet, allowing customers to be fully in control of their wallets at all times.
This part sounds to good to be true, without any details, i would assume the bank either :
1. generate private key and give it to user
2. giving user closed source wallet and send the private key to their server
Even if they don't, user's privacy is lost because they know all address and transaction of their users. They'd refuse sign transaction if users don't give details of transaction he/she want to perform.