We were two couples staying in Vienna for a few days.
Somehow we were sure there are two separate rooms with a double bed in each one, but unfortunately there was only one small room, and two beds were placed there in opposite corners, leaving almost no room to walk. Of course, it wasn't very convenient to sleep together in one room.
The apartment rules state that you must use the washing machine to wash dishes, and there's no soap for hand washing anyway, which was a bit of an inconvenience as well. We had to turn on the washing machine even to wash 2-3 plates and a few cups.
The water boiler (in the shower) was set to rather low temperature, and the warm water was only enough for 2 people at most. Then we had to wait about half an hour for it to heat up again. I guess it should be set higher for 4 people to be able to take a shower in a row.
Otherwise, the apartment was clean and had all the necessary equipment.
The area of the apartment is quite and nice, though it's too far away from center. You can't get to the city center by foot in an adequate time, but there are a lot of public transport options available in 10-15 minutes walking distance.
The owner waited for our arrival for check-in, and explained everything to us regarding the apartment and its area. He had a folder with printed maps of all the local necessities - food stores, restaurants, public transport, etc. It was very nice of him.
Overall the say was okay. The apartment ideally fits for two people, or a couple with a child, but it becomes uncomfortable for more than that. We definitely won't stay as such a big group there next time, but for smaller groups it's a good option.