In a word: fantastic
From the very second you book the room Tia and Mike are very communicative and informative about location, the automatic check-in instructions and whatever you might want to know about the apartment.
The check in sounds a lot more complicated than it actually is the first time you read it. When you get there it is very self-explanatory.
The apartment and room were incredibly clean, spotless in fact, with two towels and a small gift there on the bed. All the necesarry information about the apartment as well as some useful information about Athens and public transportation in the city.
Another thing that I really appreciated was the possibility to wash my clothes in the apartments washing machine.
Very central, a single metro stop away from the Acropolis (10 ish minutes walking distance) and 2 (20-25 minutes walking distance) from Syntagma square. While I did buy a few 24 hours metro tickets it is very easy to simply get around town and to the aparmtent by foot, which I did several times.
If you are looking for a comfortable, reasonably priced and central apartment, then look no further!