I enjoyed my week in this apartment. It was clean (especially knowing we were ~10 people staying in it!), and the room is quiet (and I you want to sleep with the windows open then Wiltrud provides earplugs). The room is spacious enough for one person. The instructions of the apartment (how to use the kitchen, bathroom, how to dispose of your waste etc...) are very clear, and Wiltrud kindly gave me informations concerning the transportation system in Vienna.
The apartment is 2 minutes away from the Subway station, and the subway brings you in the city center in a matter of minutes.
Overall I really recommand this apartment if you want to stay in Vienna for a short time like I did.