Staying at Klaus' place was really great! The location is about 10-20 minutes by U Bahn or S Bahn to basically anything you'd like to see in Berlin. The neighborhood is incredibly beautiful and quiet, there are two grocery stores within the same block, and the subway and train are right across the street. The apartment itself was comfortable, clean, and Klaus was very generous. The price, too, was more than reasonable. I would highly recommend this place!