I had four wonderful days spent in Vienna. The apartment has all the amenities I required and is very close to public transportation ( about 1 or 2 minutes' walk).
Christian is a wonderful host and he gave me some very good suggestions about where to go for concerts and operas, which led me enjoy the best performances I be ever watched in my entire life at very low prices ( only 4 euros maximum).
In a word, I highly recommend Christian, especially if you are a lover of classical music.