My girlfriend and I explored Vienna at the beginning of November and slept in the flat, which probably belongs to Juan's girlfriend, who is currently doing a semester abroad. The communication was great and the keys were handed over by the sister of the flat owner. A very nice woman who offered her help at all times.
The location is great and it's easy to get to all corners of the city by metro or tram. Bakeries, cafés and drugstores, in fact everything you need, is nearby.
The flat itself is small and fine for an overnight stay. The kitchen is very small and probably not very suitable for cooking, but we didn't try it out.
The bathroom is also small, but it is perfectly adequate. The flat has central heating and you have to wait a bit for hot water to shower if the central heating is not turned up.
As the flat is at the back of the building, the nights are quiet and there is also a lift, so there is no need to walk the 5 floors.
All in all, it was a nice stay and we can highly recommend the flat if you are only travelling in the city anyway and just need a place to sleep.