we had a mixed experience with our stay. Good thing first, the apartment is at excellent location, most of major attractions and metro station are walking distance and apartment is professionally cleaned and managed. you have lot of travel related books from lonely planet which help you to plan your next trip :-)
few things which we didn't find convenient are
This is a very big hall ( looks like a showroom converted into a house) comprise of everything i.e living room, bedroom kitchen etc there is no wall or separation, you feel like living in IKEA model house :-), bed and sofabed are next to each other. The toilet is very small and cupboard above washbasin is too much projected, all of us struck our heads while brushing.
another important point, that you must check-in before nine PM, we got delayed by few minutes and we have to pay 20 (twenty)EURO for late check-in even through we told Francis that we are getting delayed due to traffic jam in freeway.
Also pls. switch on Mosquito repellent even you don't see any, we didn't do; night woke up with mosquito humming sound and bite and it took couple of hours to get rid of Mosquitos
The entrance to the house is confusing initially but you get use to after couple of times.
we were in April which is not summer in Athens, so apartment was comfortable but I am not sure whether one Air conditioner will be sufficient to cool such a big hall. We also found AC bit noisy, it would be great if Francis can fix, it becomes annoying during night while you sleep