I had a very nice stay at this place close to Karlsplatz for almost a week in Vienna. The apartment is located in a beautiful and centrally located area and is in itself like a historical building with high ceilings and heavy wooden doors. The room is located on the 3rd floor with no elevator and long stairs.
While I have no criticism for the flawless communication about check-in and the perfect location, the walls of the room were quite thin so one can hear rather clearly what goes on in the kitchen. The room also can get a bit cold and stuffy due to its size.
All in all I very much enjoyed my stay and would gladly recommend it.