Well, it was really a unique experience, not in a good sense though.
Although it was not my hosts' fault, it turned out there was renovation works in another flat in the same apartment and workers were starting drilling and breaking at 6AM.
After making Mike aware of this unpleasant situation, he was kind enough to offer me a full refund - which unfortunately was not much helpful as I had to make a last minute booking at a hotel during bank holiday so ended up paying double.
But if I leave this disturbance aside, I can say flat is really nice, located right in the central area - so you must anticipate street noise till 2am but considering you are staying in the heart of Athens this should not be an issue. Being in walking distance to many touristic spots, cafe's and restaurants definitely overweight some noise. Also Mike was really helpful and did his best to accommodate us, it was mutually unfortunate that the construction works were taking place while I was staying.
Speaking of, not directly related to this flat but realising there are many airbnb conversions in old buildings, I recommend anyone plan to visit Athens to double check before with their host that there is no such works happening at their dates.