We had a fantastic three-night stay with our two sons (ages 7 and 11) over Easter weekend. The apartment is large, with two sizable bedrooms and a large living room, and has a rather grand old-world feel with modern updates. The kitchen was well-stocked with cookware and flatware. Christina Pia-Marie & Madel were very responsive ahead of and during our stay, and were flexible about check-in procedures.
The location is fantastic. A Spar supermarket is downstairs for any grocery needs. The apartment is located steps from two tram lines that provide excellent connections to the city center and other areas. A bikeshare station is located across the street. There are some very good restaurants within a few blocks, and it's a relatively quick walk to dining and shopping destinations in Neubau and Mariahilferstrasse.
The neighborhood was a great choice for us... good restaurant and retail options nearby, but relatively quiet and great for families. There is a park with a playground just behind the building, and our boys had a great time letting off some steam there.
The apartment fronts onto Josefstadter Strasse, so it can get noisy during tram operating hours (~5:30 am to ~11:30 pm) and some early morning recycling pickup. Otherwise, this was a pretty ideal spot to base ourselves during our visit to Vienna.