We have stayed in Christoph apartment for 5 nights, and they were marvelous.
Christoph and Ramona were so nice, they waited for us to reach the apartment despite the delay of our plan, and their welcome was so warm.
At the end of the journey Christoph helped us in getting a taxi, which made our trip to the airport much easier, he also helped us whenever we needed a certain restaurant.
The apartment is very nice, very comfortable and smartly designed. The stop of the tram line 0 is just at the door of the building. This line passes in Wien Mitte station and other big stations also.
You should visit Vienna, and certainly you should try out this apartment.