Martin's place is in a great spot. Not only is it just a brisk 10mins walk from Rathaus, but if you don't feel like walking there are 4 trams and a Bus that will take you to the city, Vienna's shopping street Mariahilferstraße, Josephstädterstrasse, Naschmarkt, Westbahnhof and more. In fact, we started calling the 13A the 'magic bus' as it stops right outside the apartment and takes you to all the major spots.
As a former Vienna resident of 14 years, I cannot fault the location.
The apartment itself is cosy, with easy to control Central heating, speedy Wifi and a washing machine. It is definitely on the smaller side with a shower curtain for a bathroom door which might bother some but we weren't really missing anything throughout our 4 weeks' stay.
Martin was quick to reply to the very few questions I had but we didn't have any issues at all.