Constantin's place is beautiful and feels very much like home and it is a very peaceful space. The bedroom is a lot bigger than the photos suggest too, with a desk, reading chair, cushioned area for sitting by the window, as well as a bed. Constantin himself is a very helpful, friendly and interesting person.
A quick U-Bahn ride to Warschauer Straße opens up a lot of transport options. A warning that there are a lot of stairs which are a bit difficult with big bags, but this is worth it as there are lovely views from the apartment.
I really enjoyed my stay, it was very restful.