My wife, 2 year daughter, and I had a great week in David's place, and we highly recommend it. David's place is about 10m drive to the city center, 2m from the tram, and 10m walk from the U-bahn. There's a grocery store and a playground around the corner, and the apartment is a nice, normal area.
David responded quickly to our WhatsApp messages, and he was very patient when our check-in was delayed by the airport nearly losing one of our bags. The inside of the apartment is great--2 fairly spacious bedrooms and a big living room. If we ever stay in Vienna again, we'll check to see if David's place is available.