I never met Ralph in person since I was the last one of our group to arrive, but he was very easy to deal with and accommodating to our needs.
The place is nice, clean and huge. We were a group of 7 and it never felt crowded. Also, the place is perfectly soundproof so we never disturbed each other when we got home different hours. We found the place a bit chilly though, especially in the living room, guest might want to bring an extra sweater.
The neighborhood is awesome! Vibrant and lively but friendly and safe. Close to public transport so the rest of Berlin is only a few minuets away.
I'd definitely stay here again, and recommend it to others traveling in a group.