We have had an excellent experience with this apartment.
First, it is located more than conveniently - it is close to the very center of Wien, and we could reach all places we needed to explore the city (including all main museums) by feet in 5-20 min. 6 min to St. Stephen Cathedral. A lot of shops, supermarkets (especially recommended is Merkur Hoher Markt, 7 min by feet), restaurants - also in the immediate vicinity. The neighborhood is pleasant and pretty silent. And 10 minutes by feet to the train station - CAT train takes you from/to the airport twice an hour (xx:06, xx:36) in only 16 min.
Second, the property itself is clean, has a lot of space, all amenities, fast and smooth wi-fi. The bedroom, the living room, the kitchen, the bathroom and the anteroom are all large. The kitchen is equipped and very convenient. The building itself is old-style and very well maintained.
And third - Anna and Vladan are great hosts, flexible and ready to help. We thought we could have issues with arrival and departure hours, but they solved all potential problems for us.
Finally, I would say this is a most recommended stay to explore Wien.