We stayed at Martin's apartment for 4 nights in July and were very pleased. The whole apartment (incl. the bathroom) was extremely clean. Martin surely does have an eye for good interior design, as he managed to create an atmosphere which made us feel "home" and really comfortable from the first day (incl. slippers to keep our feet warm).
As Martin was off on vacation himself, we met up at the apartment with his friend Fabian, who was really nice and answered all of our questions.
A big plus point goes out to Martin & Fabian, as we were able to "checkin" at 9:00 in the morning. You don't get this kind of a service at a hotel. ;)

It was a pleasure staying at your apartment, Martin. I would highly recommend this place to anyone traveling to Berlin.