We spent a whole month in Alex's apartment. Alex is a great host who is easy to communicate with and ready to solve all possible issues immediately. The apartment is clean and well equipped, also with some basic products like coffee, tea or olive oil. The place is just a few minutes walk from metro station (and then only 2 stations from Monstiraki Square) and just walking distance from Exarchia.
Wifi works great what was essentail for us to work remotely with no problems.
Just keep in mind that there's very little sunlight in the apartment. It's very common for apartments all around the city and it must be a blessing during summertime, but if you planning to visit Athens during the winter and for longer stay, you must be prepared for it.
To sum up, cool place with a great host, perfect base to explore the city.