We stayed with Guido for 5 nights in Florence. The place is located in a fantastic neighborhood, just a few steps away from the Basilica di Santa Croce. All the major sights are easily walkable under 20 minutes, including the Duomo, the train station, Uffizi Gallery, etc.
The apartment itself was clean and spacious, with plenty of room for all of our belongings. Just be warned though that the apartment is on the 3rd floor and there is no elevator, so be prepared to carry luggage up a few flights of stairs if needed.
Guido was incredibly helpful and responded to all of my questions almost instantly. He made our stay so much more enjoyable. If you are visiting Florence and looking for a great place to stay, I can't recommend Guido's place enough!