If your looking for a reasonable central location with good connectivity it would be hard to beat.
Security for main entrance to apartments felt quite poor but after a few days in Vienna iam not sure that you really need it.
3.5 flights of stairs may not suit everybody.
While the brief encounter we had with both host represents was good, who we were meeting kept changing and the two text messages sent did not get replies. Possibly a very laid back attitude to hosting which could be a problem.
That said we really enjoyed our whole vienna expierience and would be happy to stay here again and recommend it to friends.