We had a perfect stay in Vienna. The apartment is really great, cool design, well located, only a 5 minute walk to the next subway station. The bed and in particular the sofa are super comfortable. Dealing with Krzysztof was very easy. We exchanged some mails before the arrival and Krysztof responded promptly to our questions.
Also during our stay he was easily reachable on his mobile and gave us some good advice on restaurants near the apartment.
We definitely recommend Kryssztof's apartment and would stay there again on another trip to Vienna.