We had a nice stay in Harriet's place. The flat is impeccably clean and very comfortable. Harriet kindly provided us with a cot for our baby girl and there was plenty of space in the living room for the whole family to relax. The one thing I think could be better is if there were basic ingredients in the kitchen for the guests to use. Most Airbnb places we've rented provide olive oil, salt , sugar, etc, so you don't have to buy these things when you want to cook. After all, it's not very common to find travel size bottles of olive oil in the supermarket and it's a waste of money to buy a big packet of something you're only going to use a few times.
The location of the flat is good, near parks, tram lines, busses and the metro but it's not central or near anything touristy so if you are only going to be in Vienna for a few days perhaps you want something a bit more centric or lively. This wasn't a concern of ours since we've been to Vienna before and were really just looking to have a nice, quiet holiday with our kids.
Oh and we never met Harriet but she was constantly available via email and was very prompt to answer our questions.