We stayed here for four nights with our two kids, 10 and 14. It was perfect for our family of four. Even thought the apartment is small, it didn't feel cramped at all. The bathroom was roomy and the loft-bed set-up created rooms within the room. The kids loved it. Very comfortable beds and nice toiletries in the bathroom.
We really liked the creative/bohemian area. It's in the heart of Sammariterkiez in Friedrichshain, with a few cafes and restaurants nearby. For coffee and pastries, we recommend Backaro. There's also a good pizza and pasta place around the corner, Papaleos. Salami Social club also has great pizza and beer. The flat is less than a 15 min walk to Boxhagener Platz, where there are more cafes, restaurants and a weekend market. From the flat, it's an easy walk (less than 10 mins) to the U5 subway, which takes you to Alexanderplats, Brandenburg Tor and Museum Island.