Me and my friend had a great stay at Karsten's flat. We got to see Karsten only at the check-in but he was nice and friendly and took care that we had everything we needed. He also gave us a tip for a nice restaurant nearby (his guidebook tips are worth to try, too!).
The room is spacious and the bed is really comfortable. The apartment is beautiful with its high ceilings, and the kitchen and the bathroom are well-equipped.
We really liked the vibe in the neighbourhood: there are lots of nice restaurants and bars around but it's still not restless there. It is also very easy to travel from the nearest train stations to all around the city.