I had a lovely stay at Kerstin's place while I was in Berlin. The central location is great and the neighborhood is full of shops and restaurants.
Do be prepared for climbing stairs as the private entrance to the apartment is on a fourth floor walk up.
As shown in the photos the bed is at the top of a very steep ladder. Getting in and out can be tricky. There is a futon sofa in the main room that perhaps could be made up as an alternative.
But if these two notes aren't a deal breaker then I highly recommend this apartment.