Staying at Alexander's place was overall a very good experience! Though I couldn't meet him in person because he was out of town, he is very friendly and responsive by text. I also had a really good contact with his friend Anna who took care of the place in his absence.
The location is perfect to enjoy as well local Neukölln as Berlin as a whole (very good transportation). The room is large and bright, we loved the balcony. The convertible couch is comfy but its parts don't hold together so well in my opinion, which was the only inconvenience we had. Also the cleanliness could have been better, but our situation was specific as a number of guests came in a row for a while without Alexander being there, so I don't blame it on the host too much.
I definitely recommend this room!