The unit is completely standalone, with its own entrance, living room, kitchen, and the bathroom and bedroom. However it is currently (as of the time of my stay, Dec. 2017) being renovated since a permanent tenant just moved out. The light in the living room doesn't work, the toilet is a little wonky, and there are some patches where damage has repaired but the walls haven't been fully repainted yet. This was totally fine for me since, even without me asking for them, Umberto sent me lots of pictures to confirm that it was ok with before he accepted the booking. Communication was excellent and very fast.
The furnishings are nice, it's good to have a kitchen (with utensils/dishware, plus tea and coffee and cookies), and the windows offer a nice view. He and his wife (I think?) are really nice and helpful. They live in the unit just below, so they said I could ask them if I had any questions.
The apartment is also in quite possibly the best location for all the tourist attractions, situated close to the train station and along the major road connecting the Accademia and the Duomo. In a few steps I could get to most of the things I wanted to see, as well as some that I hadn't planned on but am glad to have found!
I'm glad to have stayed here, and would certainly recommend it.