I've been now several times to Athens, but never stayed in Koukaki. It was the best choice ever! This neighborhood is great as you have nice local flavour stores nearby, nice gastronomy with a great choice of Greek specialties. Excellent public transport connections as well as a nice park just around (Filopapou Hill) the corner with a magnificent view over Athens.
The apartment is great and very good suitable for long stay as you can work in a separate room with desk and space for all your working stuff, in my case my photo equipment. The kitchen/living room are good equipped and it was nice to cook. As well as the balcony is a great place to sit as you have a lot a nice sun because of no shadow from any building, this is really unique in this city. If I didn't move soon to life permanently to Athens, I would book it often. Last but not least; Fotini is a lovely host, always to your service, helpfully and fast in communication. Enjoy and explore Athens from here!