I stayed in Killian's apartment for four continuous months -- from the end of February to the very end of June. I was in Vienna as a visiting professor at a local university. The apartment was very good for such a long stay, and I came to know the surrounding neighborhoods very well (tips below). The apartment is beautifully designed by Killian (he's an architect); the windows and floors are of very high quality, excellent light in all the rooms, the bathroom fixtures are excellent and new, and the furniture Killian designed in the space is also great. When you arrive, the building itself can seem slightly shabby (particularly in the entry and common areas), but it's a nice building with quiet residents. When my wife and I arrived, the apartment was minimally stocked for long stays, but we loaded it up with new glassware, mugs, pillows (two wasn't enough), and some more cookware. Hopefully, all that stuff will stay in the place.
The only major issue in the apartment (and that is not unique to the apartment) is that it can become very warm during summer and spring heat waves. I was actually in Vienna to work on a project about how ill-prepared Viennese historic architecture is for its many recent heat waves. There are very little air-conditioned apartments in the city, and this apartment also does not have AC. So, be warned, if you're staying here between mid-June and mid-September, the interior thermometer can often be at 30-degrees (almost 90 degrees F). I have a disability, so heat can be particularly bothersome, and we bought a large fan to help cool the place down. But otherwise, the apartment was FANTASTIC -- especially in March, April and May --, and the heating system Killian installed works really well.
As for the neighborhood, I think it is a bit downplayed in the listing. The "18th" or Währing is a really great and very bourgeois neighborhood and that has beautiful parks and some great restaurants, Kutschkermarkt, and a Saturday market. All of this is very close. You are also very close (can walk) to Yppenplatz, and which has a more youthful and fun vibe. The Saturday morning market at Yppenplatz is one of the best in the outer-districts and there are many restaurants there as well. The U6 stop at Michelbeuren is very easy 3-minute walk from the apartment, and there are three other trains all within a quick walk. If you stay in Killian's place for a longer period, I recommend just walking around and discovering the interesting areas of the 18th, 17th, 16th and 15th districts. They are an under-rated part of Vienna and that shows you how people really live in the city.
All in all, I think this is an ideal place for long stays in Vienna. If you're in town for only two or three days, and you're a tourist with a bigger budget, you might want to stay closer to the center.