Efi lives in the apartment downstairs so it was no problem to get and leave the keys (especially since we had to leave very early in the morning). She was very helpful and hospitable (although we didn't talk a lot - there was really no need during our short stay).
The apartment has everything we needed (2 rooms with beds plus the living room with sofas), kitchen, wifi etc. The balcony gets hot during the day which is a pity (it's really big and comfy), but Athens does get a bit hot in August :)
The neighbourhood is nice - quiet residential, but with enough mini markets and small cafes around (big markets are also not too far away).
It's near to Sepolia metro station, which means it's less then 20 mins from the center of Athens (direct connection to Syntagma, Acropolis) and it took us some 70 mins to get to the airport.
On Thursday there was a huge market in the street (with fruit and vegetable stands), which was really fascinating.