We stayed with Nicos for a week and were absolutely satisfied with our stay. The apartment is very close to the city center and primary sights. It's about 5-7 minutes walk to the metro station, bus and trolley bus stops. There is a nice supermarket just two blocks away and lots of places to eat out within a walking distance.
The apartment is perfectly clean and looks like what you would expect looking at the photos. It has got everything you need for a comfy stay.
Nikos is a very nice and thoughtful host, always answers promptly and is ready to provide you with tips on tourist attractions or how to get everywhere around.
On the whole, I would definitely use the apartment again if I happen to come to Athens and recommend it to a friend.