Pretty sure this also requires the banks to then accept those attestation keys. Graphene pushes for them to do this, so you can't simply run whatever open OS you want on your device (like on desktop where you can also do online banking), you need to specifically use some third party service that then tells the banking software it's really okay to run on your device. I do find this to be a bit crappy, but at the same time it's quite amazing that Graphene has enough traction to convince many app vendors they should support an open/secure OS!