We stayed in the apartment for two months over winter. The location was perfect for us as we could walk into the centre of Athens but also be very close to Exarchia where there are lots of really nice (and cheap) cafes, restaurants and bars. It is close to the main road, but the apartment itself is not noisy.
The apartment is simple but definitely big enough for two people to live in. There is a very large balcony area that seems unusual for the area, and would be wonderful in the summer as a place to sit outside.
Sotiris was very easy to communicate with. When we had a problem with the internet, he was very quick to sort it out for us and even brought over some Christmas sweets and a very cosy blanket.
If you're looking for a somewhere to stay that allows you access to Kypseli or Exarchia, this is a good place to stay.