A comment by Jan-Lukas Else

All necessary bands in Germany should be supported. I think there's a list of supported bands on the Quectel website.
And yes, I think it might work with a powerbank, but I just tried it briefly. I think when the modem is more busy, it could draw to much power for the USB and lead to breaks. But I'm not sure about it. Maybe ask in the GL.iNet forum about that.