My friend and I stayed in the apartment two times, in total 7 nights.
The apartment is located on the top floor (7th), and the elevator will take you to the 6th floor. It's a completely renovated apartment, with a standard better than many others in the area (I used to live in the city some years ago). We were both very positively surprised. The room is not big, but when we were in the apartment we usually spent our time on the big balcony.
The apartment is located in the very center of the city, with everything you need in a walking distance. Yorgos was a great host, and would answer really quickly if we had any questions.
We will both recommend the apartment and most likely book it the next time we go back to Thessaloniki.