We just stayed in Stefan's apartment for three weeks. It has many advantages:
1) it is very nicely located, int he up-and coming 7th district with many new bars and restaurants in walking distance.
2) it is tastefully decorated, and everything is brand-new.
3) the apartment is very clean.
4) Stefan is a responsive host.
There are some disadvantages
1) the bed is rather small for two people and the mattress was not very good, so it is not so convenient for long-term stays or if your are two people
2) the apartment is rather small for two people,
3) there is no air-conditioning, and too hot for Viennese summers (luckily we only got a few hot days in there)