TL, DR: 10/10. Panagiotis' apartment is excellent, simply put. It looks much better in real life than in the pictures! 100% recommended.
Highlights: Nothing was missing: from all the cooking utensils you can imagine, coffee, tea, etc. to the tiniest detail. If you're looking for a long stay, this is also a great option. My favorite thing was Panos' taste for interior design: the flat is really beautiful and truly unique, as he made most of the pieces. It's very inviting. It was also very clean and functional. The location is amazing, everything is within walking distance and I didn't take the metro once in my whole stay. The communication with Panagiotis was great and everything was smooth and easy. He is truly reliable and also very friendly. He made our stay fantastic, I don't have any complaints.
Downsides (if any): The internet speed is ok, but not super fast. If you're planning to work remotely, perhaps you should consider going to one of the cafés nearby (there are plenty with good wifi in the nearby streets). I felt it was good for navigation but my Zoom calls were sometimes interrupted. The flat can get a bit noisy at night, especially during the weekends, as this is also a very busy area with bars and such. By staying in this area, this is what you sign for :) this means you can also enjoy the places without having to walk for a long time. If you sleep in the room, the noise will be fine, but if you're sensitive to loud noises, the sofa area might be a bit too much.
All in all, this is a fantastic place and I strongly recommend it. When I go back to Athens I already know where to go!