The apartment is very clean and confortable, no problem at all on this. The host is also very helpful, kind and reactive.
Nonetheless, I think I have to give more details on the neighborhood and the building itself as I would have loved to get more information myself before booking.
Omonia is one of the most dangerous neighborhood in Athens (criminality, prostitution, drugged people) and is clearly not safe especially for women travelling alone. Although the apartment is located itself in the safest part of Omonia, I cannot say we felt safe, we've seen several totally drugged people and the neighborhood is dirty and in bad condition in general. The building is also in bad state: no lights on the stairs, broken elevator, the doors are almost never closed and are in a very bad state and all the apartments on the street are abandoned. We did not use the balcony as the view is...on an abandonned building.
So to conclude it's a cheap way to visit Athens and a pretty central location to visit everything but I cannot say this is one of the best place I have been :( .
Knowing that we still enjoyed Athens a lot and we just want to be transparent with future visitors :)