Great little place if you want to be close enough to the city centre but not in it.

Viktor was always quick to reply to any queries and was very accommodating before and during our trip.
Less than 10 mins walk from Vienna Mitte, so getting to and from the airport using the S7 train was easy enough, took about 30 mins and a lot cheaper than most of the other options if you are solo or duo travelers.
No.1 Tram stop right next to apartment but we never used it as we like to walk a lot.

While others have commented on the church bells, we did not find it too much of a distraction as were up early and home late. (Not that Viktor can do much about it anyway, other than climbing up the tower with a giant bag of cotton wool and a determination to muffle it).
Alternatively a set of ear buds will do just the job. ;)
At no point did we feel unsafe in the area. Remember to stock up before you go out for the day (there were a few shops/supermarkets right next to the apartment which open early) as most grocery stores in Vienna close at 8pm. If you are arriving late, might be worth trying to get some essentials at airport if possible.
All in all, it was a perfect little apartment for our needs .