Karsten's home is nicely furnished and clean, and the room has a nice and huge bed with high ceilings. It is a 5 minute walk from the S and U-bahn stations which makes the home relatively convenient.
Karsten was nice as well, although we only met him once during check-in.
Our only gripe is the stairs we had to climb to get to his place (not the most convenient if you have heavy luggages), and the lack of lighting in the stairwell when it gets dark. It is literally pitch black as you enter the building to get to the flat (using the torchlight function on your phone would be recommended).
Other than that, our stay was great and the neighbourhood largely family oriented.