This is a spacious room in a fantastic location, easy to access by public transit and in the middle of one of the most vibrant neighbourhoods of Vienna.
I stayed there six nights. Klaus welcomed me warmly. He works at night, so we hardly had a chance to see each other after the first day. I briefly crossed paths with Simon a couple of times--also a very nice guy. In general, I had the feeling I had the apartment for myself most of the time (which at times was an advantage: the apartment, for instance, has only one bathroom, so there were no queues there!)
The only (small) issue is that the windows overlook Westbahnstrasse, a rather busy street. Trams drive underneath the window from very early in the morning to late at night, so be ready for some noise. In general, the windows are well sound-proof: if you keep them closed at night you won't hear much. But my stay coincided with some very hot days, and I needed to keep them open at night to let some fresh air cool down the room. This was a little bit of an inconvenience, especially during the weekend when the night life of the neighborhood is at its peak. An easy way to solve this issue would be to provide the room with a fan, something which I would invite the hosts to consider.
Overall, this was a good accommodation. I would recommend other AirBnb users to consider it.