Franziska's apartment was perfect for me. I stayed there for ten days. It's nothing fancy, but I appreciated the well-equipped kitchen (2 burners, a microwave, plenty of dishes/silverware/pots and pans/ways to make coffee). The apartment also had a washer/dryer, which would be useful for a longer visit. I did not experience the problems other reviewers mentioned. I took relatively short showers (5 minutes), and there was enough hot water. There was certainly no problem with ants -- the apartment was very clean. In addition, Franziska provided a nicely detailed booklet with information about the area, recycling, house rules (e.g., no smoking), etc.
I also enjoyed the location. I was in Berlin to do research. The Bundesarchiv was just around the corner, and the Geheimes Staatsarchive was a short distance (Bus M11) and the Staatsbibliothek was a direct bus ride as well (about 40 minutes on the M85 to Kulturforum). Shopping at Schlossstrasse was also an easy trip on the M85. I would stay at Franziska's again even if I planned to do more touristy things in downtown Berlin. The neighborhood is one of Berlin's wealthier and safer suburbs, but was still provided easy access to the Mitte. It was only a 25-minute cab ride from Schoenefeld Airport (and I suspect a similar distance from Tegel).
In all, staying at Franziska's was an excellent experience.