Staying in Katharina's apartment was great, we had a flat only for ourselves (couple of two) with everything that we needed and even more. The location is in a walking distance to the city center and to Mariahilferstrasse stores and restaurants. The location has also easy access to the public transport, very close to west train station and not too far (4km) to the Wien main train station. The apartment was very clean and the communication with the host (Katharina) was perfect, she is a very nice person, very welcoming and with a big pretty smile on her face ready to help you whenever you feel in doubts.
I would definately recommand this location to others, next time when will visit Vienna this one will be the first choice for us.