The Airbnb is great. We highly recommend and would stay again if we return to Firenze (and it's available). It's close to the main train station, and communications were easy with Cosimo and his girlfriend, who met us because Cosimo was unavailable at the time. They made fantastic restaurant recommendations, including Tratoria Sergio Gozzi (only open for lunch) and Antico Fattore, where Cosimo even made a reservation (and we ate La Bistecca).
The Airbnb itself is lovely and worth the walk up to the fourth floor. The windows offer an excellent view, the furnishings are useful and attractive, and the beds are comfortable. A manual provides loads of useful info, ssuch as how to use the washing machine. The Airbnb was a little chilly in late November. It's not a sleep issue as the beds have great comforters, but the floors are hardwood and tile, and the space is kept around 18C (about 65F) at all times. I brought and used my wool socks.