I'm originally from the US, but I've lived in Prague for a decade and have been traveling to Vienna 1-2 times per year. Tristan's place is by far the best I have stayed in. He is very easy to communicate with, readily provides tips regarding public transport (plus sightseeing, should you need), and is very hospitable in general. The flat itself is in a great location, spotless, and has every amenity one could want. I highly recommend and will stay there again in the future!