We had a great time in this flat !
The windows do not open on the street, so it is indeed very calm.
The location of the flat is perfect : it is really near the centre ! (2 minutes away from the Duomo, really!). The flat is very well equiped : the kitchan has everything you need if you want to cook, the bathroom is perfectly clean and new. We really felt like at home.
There is also a binder that contains verything you need to know to enjoy Firenze : taxi / supermarket / great places to eat... The only thing that need to be improved would be to translate this binder in english. It was okay for us since we know a little bit of Italian and we speak French, but I can imagine some people having a hard time understanding what to do in case the water heater does not work properly !
All in all, a very good experience, I highly recommend this place !