We stayed at C.'s place for visiting a concert. Christophe is a nice guy. We had some check-in difficulties, because he was hard to contact for any reason, but nevertheless Christophe seems to be reliable.
His flat is located close to the Olympic Arena or Waldbühne. Walking there takes approx. 30 min. But public transport is close by and makes it easy to get anywhere. Besides, a small supermarket and bakery store/Café is around the corner. (e.g. for breakfast)
The room is small but absolutely sufficient if you only want to sleep in it. (beds are comfy) It seems a little bit unfinished what makes it a little bit uncomfortably.
His living room seemed to be his working area as well and less suitable for hanging out with guests.
We got the impession of a quite tidy place, but with some deficits especially in the bathroom.
Make sure not to forget anything, you might only get it back for a good validation ;)