We are fully satisfied with the choice we made to pick up this particular apartment. The house is strategically located at the city centre, near a metro station and there are quite a few places you can visit on foot. The apartment was clean, well equiped, cosy and, as others have mentioned, more spacious than you expect. Frank was very helpful and eager to answer all our questions and also make a last minute modification in our reservation. The only issue we had was the relatively slow wifi which got better after the first two days.
I strongly recommend it for anyone who's thinking of visiting Berlin