Our stay in Gisella's apartment was nice. Upon arriving, Jens greeted us and told us basically everything about the neighbourhood and some tips on Berlin sights.
The apartment was clean, had big windows for lots of ventilation, and a fridge, which is nice. It's close to public transport, the U-Bahn station is about 5-10 minutes on foot, and a central one at that since it's an intersection of 4 separate U lines (U1~U4).