We stayed there for almost five months, and everything was fine. =)
We had good communication with Georgios and an associate (Theodoris) directly through WhatsApp: we could do the check-in late at night without problem, we could have a throughout cleaning of the flat every two weeks, could get a permanent vacuum cleaner, etc. (Thank you guys!) The kitchen was functional from day one (!) and is small but convenient. The flat is freshly refurbished, and the bathroom is very nice. The architecture might seem weird: it is a "deep" and "narrow" flat, and so it stays at a reasonable temperature during the summer and the winter. The balcony offers a glimpse of the Lycabettus, and you can access it from both rooms, share the space or enjoy some intimacy on your part of the balcony thanks to the wall architecture in L . The AC units in the bedrooms work perfectly. There is enough warm water all year round, and the heating system works in November. So yeah: you can perfectly live there!
A few critics: if the double bed is very comfy, the two single beds have spring mattress which is not that great when you grow older and heavier! Some neighbours can be noisy through the bathroom window, but if you close it, it's fine. There is not as much street traffic as one could fear, however it can happen that a coach loads or unloads people at 4 am close by and it could briefly get noisy. Once again, this is only if you sleep with the windows open (there is a mosquito net), otherwise it very quiet for Athens. The general neighbourhood is not that nice looking with a kind of transportation hub around and some homeless people during the summer.
However, the flat is right across the street from Metaxourgeio metro station, which is very convenient. There is also a small grocery store there, and you are one metro stop away from a big Sklavenitis supermarket. There are several street coffee shops, a delicious bakery, and some gyros places all around. A special mention to our favourite restaurant in Athens at the end of the block: the Typographos, please go there for us, we already miss the place.