I stayed in Alexander's apartment for one week at the end of August 2015. I stayed with my wife and two daughters (6 years and 23 months old).
Alexander and Bettina were very kind explaining about the place when we arrive. We just rang the bell (they live in the same building) when we reach the place, and they opened the apartment.
The place is very well kept and clean. All facilities are working perfectly including wifi, cable TV, washing machines, etc.
The place is also very conveniently located, just a stone throw away from supermarket (Spar). It is also 3-4 minutes walking distance to park beside St Karl church, where there is a playground where the kids really like to play.
Lastly, both Alexander and Bettina are really willing to help and reachable when we need something. For example, there was one occasion when the cloth dryer does not work suddenly. I just ring the bell of their apartment (they live in the same floor), and Bettina quickly identified it was because we did not throw the water that was filled up.
Overall the experience was really good, and I would stay again in the future when we visit Vienna!