I booked this studio in place of a larger one in Bergmannkiez that was no longer available. This was my fifth stay in Berlin, so I did not need to be right by the main tourist amenities (Museum Island, Alexanderplatz, Under den Linden...). There's much more in Berlin than that, of course.
All of my other stays had been in Charlottenburg or Schöneberg, but location turned out awesome: close to many bars and the subway in Kotti, in a hip neighborhood, but amazingly quiet. There is a market on the weekends where you can buy cheap groceries, plus cafés everywhere, a pharmacy, two supermarkets... Really practical. It also helped that some nightlife targets (Schwuz, Berghain) were easy to get to from here, as well as film places (Moviemento).
Regarding the place itself, it is a small studio, with a sofabed on the main space, and another bed elevated on a platform: I had no trouble at all getting sleep, and the space was more than sufficient for my needs. Neighbors are quiet, and all utilities work perfectly (I stayed there in January—not the coldest January, but cold still). I was able to cook all my breakfasts and some main meals with no trouble at all. Needless to say, the space was spotless when I arrived.
Regarding communication, Matthias was superdiligent, and arranged a way for me to get the key even when the building manager was out.
If I were to mention any shortcomings, I would only say it has no elevator, in case you have very large luggage pieces. This fact, however, is unexceptional in similar building, as far as I know (it is also a first floor, so no big deal).