We stayed for a month and I can say overall it was great experience. Apartment is nice and modern, Panos is great host, very responsive and helpful, he brought us everything we needed. Only one small nuisance was the water pressure, you can't have two people using the showers in the two bathrooms at the same time, but that didn't bother us.
Location-wise, the good thing is that it is within a fair walking distance to Monastiraki (20-25 mins), Syntagma square is around 30 mins walk, and Gazi area is also about the same time. If you prefer public transport, the metro is 3-5 mins walking from the apartment. There are a few small grocery shops and a couple supermarkets nearby, as well as a nice bakery. There are even some restaurants that have ready-made cooked food that you can take away.
The bad side of the location is that the area is not safe! Please take extra care of your belongings if you walk the streets, avoid small streets at night, there are pickpockets even during the day! Also, even though there is a free parking in front of the building, I advise to use a paid parking garage. There is one nearby.
So all in all, I do recommend the apartment, only take care of yourself when you are outside!