Philipp's flat is great and stylish, and a lovely pad to spend more than a couple of days in Berlin. There's everything you need to cook, a great bathroom and a very nice living room with high ceilings.
However, access is not great - if you have mobility problems, look elsewhere, as you'll have to climb 6 flights of stairs. To be fair, Philipp does not hide this in his description of the place, just keep it in mind.
This area of Berlin is a bit shabby and dirty, but we never felt unsafe and Philipp gave us brilliant local tips.
Go ahead and enjoy Berlin!