For location, this place near the centre of Athens is unbeatable. It's tucked away from the crowds and in a relatively quiet back street.
There is a great bar round the corner, some excellent neighbourhood cafes and a really good bakery on the next street. There is a cool vegan street food hole-in-wall place just 5 mins away which is (relatively) cheap and tasty.
As a few people have mentioned, the apartment isn't huge, but for 1-2 people it's fine if you plan to be out and about. If you're visiting Athens for a short trip it's very convenient, especially with the entrance to the Acropolis only 15 mins away and the Acropolis Museum a couple of streets from the flat.
Communication with the owner was all good, zero problems checking in or out. Thanks!