My wife and I spent 3 days in Silvia's apartment. It is beautifully decorated and has all you need to spend a good time in Firenze. Being newly refurbished it is very clean and is big enough to accommodate 4 adults (we were only 2 :-)).
It is ideally located in the city center (you can see the Duomo from the balcony :-)) :
The pros is that you are within walking distance from nearly all the main monuments, the cons is that the Giuseppe Verdi street where it's located is a busy one and tends to be quite noisy at night (a lot of restaurants, bars nearby).
Silvia and her brother were very helpful before and during our stay. They welcomed us at the apartment and gave us some good advices for our trip (thanks again !! :-)).
So it was a pleasant stay in a beautiful apartment in a beautiful city :-)