We had a short but excellent stay at Nikos' apartment! The location of the apartment is amazing if you want to see the key sights of Athens, since it is within a 5 minute walk of the Acropolis Museum and Parthenon, a 4-minute walk from dozens of great restaurants, and a 2 minute walk from a key pick up point for 3 of the major "hop on hop off" bus tours. There is also a small well-stocked convenience store and top-notch bakery literally around the corner.
The apartment itself is simple but super clean and has almost everything you will need for your stay. The only thing missing was a microwave, but there is a small stovetop/oven unit as well as a panini maker that can be used to cook up some dishes of your own. One other minor issue was that the shower had a handheld hose instead of being mounted against the wall.
Nikos was a super helpful host, and even arranged a taxi for us from the airport. I'd definitely recommend this place if you're looking for a convenient, clean, safe, and affordable place to stay as you do the touristy things in Athens.