Karl Michael was a totally reliable and very friendly, welcoming host. We didn't actually have a chance to meet in person, but he responded to phone calls and whatsapp promptly and arranged for all details in a way that absolutely everything went smoothly. The house in which the apartment is located is a beautifully renovated turn-of-the century building, and the location is quiet, and very convenient to downtown, as well as to the Volksoper and a farmer's market. Grocery stores are also nearby, as well as cafes, boutiques etc. I hope to visit and stay at his apartment again next time I'm in Vienna!