Constantinos' apartment is big, clean and very bright, which made it perfect for myself. You can clearly see that everything was recently renovated in nordic style. I loved the big space and the bathroom.
Constantinos replied to every message that I sent in no time, which was very helpful.
Everything is in walking distance: less than 10 minutes and you are in Monastiraki, Plaka, Syntagma... so if you don't want to use public transportation, this is great!
At night the area is a little bit noisy, but you can find earplugs in the apartment.
The only thing I didn't like was that at night and early morning, the area didn't look very friendly/safe (although anything happened) so I always walked back home before sunset.
Good value for money, though :)