Nice studio apartment in first floor of a residentual block. Clean and stylish. The apartment us not located in a central area (hence the very good price) HOWEVER city centre can be reached very easilily using public transport which is cheap and reliable. My suggestion is that you get hold of public transport tickets (various options) on the very first day from the airport. To reach the airport just buy a ticket (€6) from the airport and hop in the X93 bus which will stop you at a 30 second walk from the apartment. To return to the airport catch same bus from same bus stop.
Reaching Athens city centre via public transport is very easy. Catch a bus and stop at the bus stop named Attiki (3 or 4 stops) and from there catch the metro to wherever you need. The green line and the red line are the most useful I think if you want to explore Monastiraki and Plaka regions. Green line will also take you to the port. Good connections to the suburban railway if you plan to go outside Athens.
We did not meet Antonis but check in was very smooth. He sent his friend to hand us the keys. Communication with Antonis was always quick and effective.
Overall a great experience and would recommend.