In brief: GREAT host, lovely apartment, very good location, NOT for light sleepers.
I'll be brief about the amenities and generalities - everything worked, we had just about everything we needed, the place was very clean and tidy and felt very home-like, check-in/out was easy, plenty of food and shopping nearby, centrally located, we felt we had definitely gotten our money's worth, and so on. Three things are worth mentioning:
1. Above everything else, Prokopis Doukas, the host, is a great guy. Starting with smooth telephone communication and giving us a very good bottle of wine as a welcome present through to all sorts of assistance like booking one of the best tables at a rooftop restaurant with an excellent view of the Parthenon and down to arranging cabs and parking, he was always willing to help and advise.
2. If you are a light sleeper this may not be the place for you. Traffic noise is quite noticeable. The street (Plateia Eleftherias) is not busy, but when there's a car coming, and especially a bus or a scooter, boy can you hear them! More so at night, when there's hardly any traffic but every vehicle is noticed. As some vehicles go down a cobbled street just above the apartment, this could definitely be an issue for light sleepers. However, the internal bedroom (with two beds) is much better in this respect.
3. Psyrri is a diverse neighborhood. One street is bustling with activity and has renovated houses while the next street feels deserted or slightly run-down. Areas closer to Plateia Iroon are lively and well-kept (in general) while those above Plateia Eleftherias towards Evripidou street and the Central Market are off-putting in some senses. I would definitely stay here again and keep my eyes and ears open when walking in the more run-down sections of the neighborhood.