We stayed 4 nights in Konstantinos' apartment at the end of September. It's an incredible mix between simplicity, efficiency and warmness : we loved it ! It's comfortable and super clean.
Konstantinos is very reactive and kind. We were visiting the city all day long but didn't wake up early, and he always informed us in advance the schedule he was working in his office on the afternoon.
First I was afraid about the ventilation in the bedroom but there is a patio just in front and you can make fresh air with another big window in the office. During our stay the weather was a bit cold, so it was great the room was hot.
I had not understand why a comment says to stay at Konstantinos' is highly inspiring. Now, I perfectly understand and agree ! You won't be the only travelers in the building, but you will be the only to stay at a place whose goal is "to climb your own mountains". One of our best Air bnb experiences !