We were four people and stayed in Vienna for 5 days! The flat was great! Location isn't far from the city center and a grocery store is nearby. The flat was spacious enough for all of us and really cosy! The only little inconvenience would be in really hot days it got really hot inside as well and unfortunately there was no air conditioner.
But other than everything was really satisfying! And Corinna was really helpful and seemed very friendly, and responds really fast to messages (unfortunately we did not meet each other in real as she was out of town at that time).
I definitely recommend the flat if you are looking for spending few days in Vienna :)!