We can highly recommend Christos' and Aleka's place if you are planning on staying in Athens. The flat is located in a nice neighbourhood, which can be reached easily per metro. You can reach the centre by foot and it takes about 30 minutes to get to the Akropolis this way. It is spacious enough and as advertised as on the pictures.
In particular, the communication and hospitality were great - Aleka responded very quickly to any open questions and was very helpful in any way. We would stay again at any time :).