The stay at Klaus' place was absolutely perfect. The flat has everything you need for a long term stay, and was in general very high quality (many kitchen appliances, good shower, fast wifi, very comfortable bed). There's an elevator in the building as well. The location of the flat is also great, as there's a metro station only 2 minutes away (you can get to the city center in 15-20 minutes). Klaus was a very gracious host and was always available to answer any question I had. I would gladly stay there again and highly recommend the flat to anybody looking for a short or long term stay in Vienna!