Klaus and his girlfriend Stavroula were very warm and welcoming hosts. The room and flat were as described and the place was really cool, on a street with few cars and with plenty of cafés and restaurants nearby. For me the bed was a good size and comfortable. The directions Klaus sent beforehand were very helpful and the location of the flat was excellent, within walking distance or a short underground ride from the major sights in the centre. We all stayed up chatting over a glass of wine until the early hours - great fun.
I give this place an unreserved recommendation should you want to stay in Vienna.