I stayed in Alexandra's apartment for 1 month and everything was great! The location is excellent, at walking distance from the main train station and the Keplerplatz metro station, and there are also many restaurants and supermarkets nearby. The apartmentis faces the internal courtyard, so there is no traffic noise at all.
I didn't meet Alexandra personally since she was out of town, so her very friendly co-host checked me in, but they gave me both their phone numbers and were very helpful with any question.
Considering the long stay, I also found very convenient that there is a washing machine in the apartment, and the internet connection was fast and reliable.
I would definitely consider it again if I were to visit Vienna in the future!