Sonja's place is awesome. We stayed there for a week and it was perfect for our needs. It's small but spatiously organized, clean and tidy.
The only small thing was that some sheets/towels seemed to be a bit old which made it difficult to wash dishes properly etc. The washing machine was still broken which was a pity, but we fortunately had enough clothes. I suppose this will be fixed soon though :)
What makes the place even better is the location. It's close to the Westbahnhof which makes it simple to get around the city. It also has railway connections in and out of the city and a shopping centre.
Sonja's location is perfect for travellers who want to explore Vienna and need a clean, simple place to sleep. Highly recommended.