I really enjoyed staying at Anna's place. Anna was super accommodating with check-in, I didn't arrive until around 00:30 but she still met me in person to introduce herself and show me around the flat. The flat is really nice and very well equipped. The surrounding area and the flat itself both felt very safe, which was a major concern of mine as a young, solo female traveler. The location isn't great, it's about a 15 minute walk to the U4 station and takes about 20-30 minutes total to get into the city center, but even with that I would definitely stay at Anna's again if I ever come back to Vienna.