This flat is indeed very clean, as the reviews said. Very convenient for food shopping as supermarkets SPAR and Hofer (i.e., Aldi in Austria) are virtually next door. Convenient for public transport. Very quiet in the top floor. Serge is a great host. He helped carrying our luggage to the 5th floor as the electricity is under repair just when we arrived so the lift is out of order.
Just to remind that you'd better ask for a brief demo of how to use the air conditioning controller as many icons without text maybe a bit difficult for non-gadget person.
Overall a great stay for our 5 days in Vienna! We thoroughly enjoyed it.