Stelios' flat was very clean and comfortable, with an amazingly spacious balcony. I spent two months there and it really felt like home, in a lovely quiet building with friendly people. Check in via the keybox was a breeze, thanks to Stelios' excellent instructions and photos, and he was always quick to respond to any questions or concerns.
Regarding the neighborhood, nearly every cab driver I had and every local I spoke to made the neighborhood out to be dangerous. I did not find this to be the case, particularly during the day when it's just like any other neighborhood. As a female traveling solo I made it a practice not to walk home at night, but even so I never felt unsafe being there. Is it the most picturesque neighborhood in Athens? Nope. But it is centrally located (5 minute walk to Omonia station and 20 minute walk to Monastiraki square) and perfectly fine.