We had a very pleasant stay.
Accommodation is not in the inner circle of Vienna but you'll manage to get to almost everything in under 30 min of walking.
Subway is 5 minutes by foot.
Since we've been mostly out exploring the city we didn't spend entire days or evenings in the apartment.
If you want to spend more time in the apartment i wouldn't recommend more than 8 persons, since you won't have an separate living room then.
Also only 1 bathroom, but toilette and shower are separated. That's kind of a plus as well for organizing larger number of people in the morning.
Would absolutely return.