We have nothing but good things to say about our stay at Ekaterina's place. First, the pictures online are accurate, but to avoid any confusion, the place is a true flat, not a one bedroom. Our kids slept on the sofa bed while my wife and I took the bed. You are in one big room together. (The bed was very comfortable, by the way.) There is a kitchen, and the bathroom with sink and shower is separated from the room with the toilet. This is a nice feature when you have 4 people getting ready.
Next, the location is amazing for a visitor. Everything in the Inner City is easily walkable, but what we truly appreciated was how quiet the place was so that we could sleep well. The unit faces the courtyard and we did NOT hear street noise or drunk people constantly yelling outside our window like we did in Rome and Budapest after we were told that our apartment was on a quiet street.
To wrap up on location, perhaps the best thing is to be able to take the airport bus almost directly to the door of the building. It is literally about 20 meters away! And Ekaterina's stop is the first stop from the airport. Additionally, we took the U to Schonbrunn Palace and to the main train station. You can catch it about 50 meters away at Schwedenplatz so it is also super convenient.
Finally, Ekaterina is very nice and helpful and responds quickly to messages. The place was well stocked with extra pillows and blankets, plus towels and toiletries, in case you forgot something, which was a nice surprise.
All in all, our best experience in Europe, hands down!