Apartment is located really close to the underground station. It takes you no more than 5 mins to get there. And then around 10 mins to the city center. U4 is my favourite underground line, so I highly recommend this direction. There's a supermarket 4 mins from the apartment which has everything you need for your stay. There were 4 of us staying at the apartment, however I'd recommend this place more for 2 people as sofa isn't that comfortable for a long stay and there isn't a lot of space to store many suitcases, but it was good enough for a short stay that we had. What I really liked about the place as it was really warm inside during cold days, you can adjust temperature by yourself. Another thing is that apartment has anything one can think of: tea, coffee, backing paper, paper towels, washing powder and many more. It's completely ready for you to feel at home.
Andreja is super lovely and friendly host. I'd definitely recommend her place to stay in while in Vienna!