The stay overall was very pleasant.
Apartment is very cozy and well equipped. The bed was comfortable, with a good mattress and large pillows. The location is a bit from the center, but there's an underground tram stop right near the building (no, trams are underground so you never hear them). It takes only 11 min by tram and they go often.
We'd like to additionally mention extraordinary hospitality and thank Michael for taking quite a lot of his time during check-in to answer our questions about Vienna, give us very valuable tips and even find the right train to get to the airport during check-out.