We spent 4 months in this apartment. It's a very nice place in the center of Athens, 20 meters from the anarchist heart and the rallying points during the demonstrations. Rest assured, in 4 months from September to December, and during "big events" (November and December being known as the hottest times), we were not worried once. Early in the morning, late in the evening, even in the night, the place which can seem impressive is finally very secure! (Believe us).
The apartment is very well equipped, quite dark in winter, to be honest it is good to go outside to see some sunlight! Of all the airbnb's we have done, this one is the cleanest! When we arrived, everything was perfect, the cleaning was thorough, towels, spare sheets, soap, shower gel, sponges, fruit, dishes were very clean... Everything was really impeccably cleaned.
For two people it's a really nice place, you have to be warned about the noise at night (bring earplugs), as well as the neighbor upstairs who can make some noise from time to time (for a few days/week that will probably not be very disturbing).
Costas is very nice, he was there whenever we needed him, even if sometimes we needed a reminder, we got the job done!
If you want to discover Athens in a lively place, surrounded by good restaurants and small atypical places, this is the place to go!