I spent an entire month in the flat, and at the end I asked for an extension. It has been a pleasure to use their apartment, it really made me feel like at home. Compared to most places I've been to, this one has everything that you need --especially the tools for cooking, which in medium/long stays can really make a difference. They have also been super nice with me, answering immediately to every message. I can't recommend the flat --and the lovely Neubau-- enough.
Tip for international travelers, there is a huge Thalia (on Mariahilferstrasse) at a 10min walking distance that has a big selection of books in English --and a nice Cafe inside ;)