Pros: Kerstin's place is comfortable and in a wonderful neighborhood. Far enough from the tourist areas to feel like you're among locals, but still central enough to conveniently access anywhere you want. The restaurants nearby are great - highly recommend Mama's Bahn and Spreegold! Volkspark Friedrichshain, the nearby park a few blocks away, is a lovely place to run, walk, hammock, etc. Kerstin was also accommodating - I got sick on the last night of our stay, and she generously let us check out late so I could sleep in. The place has standard furnishing, but is spacious and comfortable and a good value for the price.
Cons: The lofted bed gets hot, but a carefully placed fan and open windows helped a lot. There was loud construction going on in nearby flats most days starting around 9am. Wifi was out while we were there, and we weren't given a heads up about it though it hadn't been working beforehand. That said, Kerstin expects it will be fixed by June 8th, and she did compensate us for the international data charges we incurred without data, which we appreciate.
Overall we had a nice stay and recommend Kerstin's place to fellow travelers!