This is a great apartment for anyone who is looking for a quiet, safe neighborhood that is within reach of central Athens (20 min metro when you include the walk to the station) and doesn't want to deal with the hordes of tourists that flood the city. Ethically, I have less qualms staying here instead of Exarchia -- you can't gentrify an upper-class neighborhood, which this part of town is.
George was an excellent and attentive host; he waited quite late at night to personally welcome us to the property and had suggestions for where to eat nearby and that sort of thing.
The flat itself is comfortable for a traveling couple; I wouldn't recommend the couch for sleeping on though.
Air conditioning was a life saver with summer temperatures above 35 C / 90 F, and we somewhat guiltily spent a day indoors watching episodes of Rick and Morty on the very big HD TV in the bedroom.
The only downside (if you can call it that) is getting to the coast takes a long time, because Katehaki is so far inland. We day-tripped to Vouliagmeni beach and it was 80 min via public transport. Took the taxi on the return, 25 euro for a 25 min ride.
I'd definitely stay here again! Thanks George!