My friend and I just stayed 3 nights at Claus' place and we had a very good time there. The apartment is in a very good location- right in the middle of shops, restaurants, bars - but in a quiet street. It is very clean, well-equipped and space-wise perfect for two people.
Since Claus is an easygoing and very friendly guy, making arrangements with him for our arrival & departure was no problem at all. And he speaks very good German, too. I can definitely recommend his apartment.