The stay was very nice! Everything worked out super well for us, the rooms are nice and tidy. Also the key delivery with a friend of Stefan worked out super uncomplicated and he gave us good directions to find the flat what after all is generally not that hard. The neighbourhood was very quiet at night and we were able to sleep soundly.
Everything is super near and easy to reach by u-bahn, tram or bus and you are totally flexible once you figure out how to buy a ticket for local traffic (we had a hard time here. However, that's not related to the flat ;) )
After all we can totally recommend a stay at Stefan's when you are visiting beautiful Vienna!