The flat I stayed in (ground floor, B1) was beautiful and light, high ceilings, polished floorboards, and spacious. The staff there were very friendly and helpful. I was extremely comfortable.
For a street so close to the centre of Athens (which is a very vibrant, noisy city), it was incredibly quiet. I was working with the university there and had no problems getting a couple of half-days work done in the flat.
The property is a 10 minute walk from the Acropolis (depending on how you deal with hills!), 15 mins from the tourist centre, loads of great cafes and restaurants and many more within easy access through the metro network which is a 10 minute downhill walk. Just bear in mind that you don’t visit Athens and avoid hills! But there’s Uber etc. if you don’t like that.
I would note that the “kitchen” was extremely small, and although I cooked in it every night with no problem, if you are planning a long stay and to make your own food, you should be aware of that. I enjoy a desk or a dining table (for working more than eating), but my flat didn’t have one. That said, I still rate this 5 star accomodation because it was such a lovely space with a great feel, and the staff there were so friendly. To me, that’s what counts.