I've used Paydirekt for a few online purchases, and it's pretty smooth. But for casinos? Nah, I prefer methods with better buyer protection. You never know when you might need to dispute a transaction.
Don't forget about Betway. Had pretty good experience with their support and their casino is solid too. As for me quick withdrawals is a good bonus too.
Word of caution: make sure you're familiar with German gambling laws. They're stricter than the US in some ways. Monthly deposit limits, etc. Better safe than sorry!