Just got back from a one week stay in Mavrea with wife and two children (3 and 6 years old). Really liked the apartment (think it was apt 8) which is very spacious with two balconies to choose your view over the harbour.
Things to note are:
(1) apartments are under new management (Canadian / Dutch couple) - although don't know whether ownership has actually changed;
(2) being central there is some noise (mainly from the church bells!) but none of us had any problems with sleeping etc and car noise was nothing like that which one of the previous reviewers experienced ... maybe because Koroni now has a oneway traffic system during the summer?
(3) Its not a serviced apartment - i.e. towels are provided but are not changed during the week and you need to empty your own rubbish and clean the apartment during your stay.
We liked it and would go back again.