We stayed 3 nights and really enjoyed the apartment, and Florence.
Check-in and communication before were very efficient. Claudio's friend Denis handled it. He met us at the apartment, showed us everything in good detail, pulled out a map and diagrammed the city for us, pointing out important tourist attractions, recommended restaurants, etc.
The apartment itself was very well taken care of and up-to-date. It's located on the interior of the building, with a small courtyard in front with a table dedicated to the apartment. Being located on the inside, it's pretty shielded from outside and street noise.
The location was very good - about 10-15 min. walk from the train station, 10 min. from car rentals, a bakery 2-3 doors down, a grocery store, just down the street, restaurants less than 5 mins. away. The historic area of Florence is pretty condensed, so we found everything we wanted to see to be very walkable.
A few cons: some noise from the upstairs neighbor late at night and the internet connection was on the slow side.