I stayed in Maria's flat for about two weeks. The flat is very spacious and the big advantage over other flats in Athens is that it has enough daylight and a great big balcony. I was alone, but theoretically several people can stay there.
The flat is very well connected to public transport. You can take the metro directly from the airport almost to the apartment without changing trains. There are also two bus lines practically right outside the door. However, from my point of view, the major attractions are all within walking distance. Otherwise, the taxis in Athens are also very cheap.
Just one door away, there is a small kiosk where you can get everything from alcohol to cigarettes and food for emergencies. There is another bigger supermarket around the corner, just a 2-minute walk away, where you can get everything you need to live.
I like the Kerameikos neighbourhood very much. It is a young, up-and-coming district with many small cafés as well as inexpensive and upscale restaurants. The absolute highlight for me is the small jazz club just one door away. I especially like it because it's not just tourists, but mainly locals.
All in all, I really enjoyed my stay and would recommend the flat again and again!