We had a nice stay in Berlin. Katrin was a good host, although we did not meet. The apartment was good for the 4 of us, well equipped, modern and clean.
The apartment has one big room with a double bed, an extendable and a small kitchen.
The area was ok, about 10 minutes away to public transport (U-bahn or S-bahn).
As other reviewers noted, the street is a bit noisy (but have slept in loader Mediterranean cities).
All in all I can recommend Katrin and her place. We enjoyed our stay in Berlin. Thank you so much!