My husband and I stayed at Kostas' apartment for 4 days - it was wonderful! Kostas was very communicative, kind, and attentive throughout the entire process. The apartment itself is lovely - it has two balconies, one of which overlooks the city and has a clear view of the Acropolis. The neighborhood is quiet and quaint, and near both the Metro and the main train station, which was perfect for our day trip to Meteora (highly recommended!) The place was clean and quiet, and Kostas has a convenient folder of things to do around the city. We also used the washing machine, which worked well.
We'd be happy to stay here again next time we're in Athens. Highly recommend.