For anyone else interested in this, I picked up that Blau card (here's an
active ebay listing from the same seller). I got a nano SIM along with the PIN/PUK and all the info to log into the account. I haven't been to Germany yet to try it for real, but I popped it in my phone here in the US and it connected to AT&T. I tried to send a text and I got a text from Blau saying I need to top up before I can do that, so it looks like everything's in order.