Birgit was super fast answering the questions and was really helpful, however her friend, who met us at the check-in, didn't speak a single word of english, and it was pretty difficult to understand her, but that was not a big problem. The apartment is nice and quiet, the building looks a bit scary and half abbandoned, but the inside of the appartment is perfect, very clean and well equipped.
The subway station is 20m away from the appartment and there are a couple of supermarkets nearby, so the location is very good.
We stayed there for 6 days and I can recommend it to anyone who wants to visit Vienna, we will come back!