This is an lovely, convenient flat with a friendly and helpful host, Carlo (è un appartamento carino e comodo con un ospite - Carlo - simpaticissimo e molto disponibile).
We found the flat exactly as described a short, easy walk from Santa Maria Novella station. Carlo offered a warm welcome and had plenty of suggestions for places to visit and eat. There was a bottle of Chianti as a 'housewarming' gift, which went down very well over dinner one evening.
The flat is near a few fun little bars and restaurants, but courtesy of double glazing (triple when you factor in the extra internal windows) there was very little noise from the street. The air-con was a godsend given that daytime temperatures were in the 30s during our stay, and we stayed cool and comfortable indoors.
The handiest thing was being so central so cheaply and having the option to self-cater, which we did for a couple of meals. The location means you can have a splashier night out (there are plenty of good restaurants and bars within a 10 minute walk, including Centopoveri and Il Latini, and my favourite cocktail bar in the city, L'Antico Café del Moro aka ArtBar), or a more budget break.
The river's 2 minutes away, and being slap bang in the historic centre none of the major sights are more than 15/20 minutes (max) walk away, which was ideal and we managed to see a lot of the city in a long weekend, while easily being able to pop home to rest our feet/eat/have a nap. We'll definitely be looking to book this flat again next time we come to Florence.

If you happen to be in Florence this summer, I can't recommend highly enough a late visit to the Palazzo Vecchio (open until 11pm, last entry at 10pm, at the moment). You'll have the place almost to yourself and there's often life music in the Piazza della Signoria outside, which lends a certain magic to the visit.