I can't fault this place or the hosts, it was perfect in every way. The location is fabulous - less than 5 minutes to the metro and then you are in town in about 10 minutes. It is also easily accessible form the airport. The apartments themselves were outstanding (we were there as part of a large group, so had booked 1-bed apartments, a studio and a 3-bed apartment) - each was large, modern, clean and extremely well-presented with every amenity you could hope for. Although the building is on a main road we heard no noise at night so slept very well. There were two small children in our party and the hosts provided high chairs, cots, baby baths and even toys. The service in advance of our stay and while we were there was superb - I had to make several changes to the booking which were all accommodated rapidly, questions were answered immediately, and the check-in / out process was very smooth. We also had mobile numbers for all the hosts during the stay for any problems or questions (although we had none, since everything in advance had been so thorough!) We were also given recommendations for the local area, including directions to the supermarket which was a 5 minute walk. We didn't explore the immediate area too much as we were in Vienna for a wedding, but there were some nice-looking bars and restaurants on the doorstep, and the Danube and a large park are very close.
When we are back in Vienna we will definitely stay here again!