We had a lovely stay at Robin's flat. The apartment is really cosy, well-equiped, clean, functional and the balcony was the small bonus.
Very well located in Friedrichshain, close to the metro station. The apartment and the street are very quiet, and in 5 minutes walk you get close to a lot of bars and restaurants.
Also, Robin has been very convenient for the check-in and check-out.
I would definitely recommend a stay at his place which will make you feel really comfortable in Berlin!