The flat is directly across from Mercale Centrale which is a fabulous market – and San Lorenzo is a great location as it's close to the train station, Duomo, Uffizi, Tornabuoni and a 20 minute walk to Ponte Vecchio. You can walk everywhere and you should in Florence. You can get to Sant'Ambrogio which has a more local vibe on this side of the arno, Santa Maria Novella, and Palazzo Pitti.
The flat itself is very clean, comfortable and looks exactly like the photos. As far as the stairs that were mentioned in the other reviews, yes they are narrow and there is no elevator but that is standard in Europe, especially a city like Florence.
I would absolutely recommend this flat!