I stayed with three colleagues at Daniel's place during a work event. The location is great, a couple of minutes away from the tram that takes you to Rathaus, and it is within walking distance from the city center. Near the appartement there are many restaurants, bakeries, cafes and shops in a really nice district.
The appartement was cosy and clean, we loved the common room and the awesome speakers for a bit of music before going out :)
Daniel was very quick to reply throughout our stay and although we haven't met, we managed to arrange the key pick up and drop off despite some scheduling issues:)
I would recommend his place to anyone looking to see some other lovely parts of Vienna apart from the strict city center:)