Kostas is a wonderful host and his place is great. It is small but very comfortable and quiet, well equipped, and has excellent wifi. It is beautifully private, including the terrace which has perhaps the best view in Salonika.
The one thing to be clearly aware of is that the building has no elevator and the apartment is on the top floor--40+ stair-steps up. And this is after you reach the door of the building itself which involves a significant climb up more steep steps outside. None of this was a problem for us but anyone with significant luggage and/or difficulties with stairs should probably find somewhere else to stay.
We hope to be able to stay in Kostas's place when we come back next year.