First, Alessandro and Azadeh are excellent, make that outstanding, hosts. For us, the critical junctures with an Airbnb stay can be the check-in and check-out. For example, sometimes a keybox to access an apartment in an unfamiliar building can be a challenge. A&A were "on top of things" at both of these critical junctures. They helped with the move-in and explained the ins and outs of the apartment. Similarly, at check-out they were very helpful in arranging transport to the airport (not necessarily that easy in central Florence). Although we had no reason to contact them during our stay, I am confident that they would have been very responsive.
The location of the apartment could not be better -- literally 100m (maybe less) from the Duomo, the center of historic Florence. The apartment itself is fine -- AC works great (an absolute necessity in August in Florence), and the other appliances also worked well. Bed was comfortable, and so forth. Sparkling clean. The apartment is an interior unit (which works well for noise control -- we heard none despite being in the center).
Our only (mild, slight) reservation was the view. Not bad -- the windows do not look out at buildings -- you see plenty of sky -- but there is not much of a panorama. Nevertheless, we did not spend that much time in the apartment -- we were in Florence to see Florence.