Me and my partner stayed 15 days in Tèo's apartment in Kypseli in Athens over Christmas and New Year’s. We only needed a place to sleep as we have an apartment just next door. For the price, Tèo's apartment is a great value for money. It is small, but it is nicely renovated and has everything you would need. Kypseli is a vibrant neighborhood - a bit outside the center - but you can reach the center by taking a 20-minutes walk to the Metro station Viktoria.
All in all a great apartment if you are looking for a small and affordable place. There were a few negative sides, though, the apartment is a bit cold and humid in the winter. The apartment does not have radiators; the air condition it has may be fine for summer, but it can hardly warm the place. The apartment is in the first floor and has little daylight, and also lack curtains so when you open the window shades to get the most of the daylight into the place as possible, you are quite exposed.