Lovely flat in a wonderful location! Uma & Tina are awesome hosts, with great advice and sweet gifts (biscotti made a surprise appearance!) to share. It's a quick 15-20 minute walk from the main train station and 5-10 minutes to the city centre.
However, the key advantage, in my mind, is to be just outside the city centre and away from the tourist hubbub! One minute away, there's an amazing little bakery (sign says 'Panificio' and the door says 'S.forno') with incredible fresh bread, pastry and dairy. 5 minutes away, still south of the river, is some of the best coffee in Florence, at the gorgeous cafe Ditta Artigianale. Piazza Santo Spirito, the local hang where you can sunbathe/read/eat/drink, is similarly close by, as are the Boboli Gardens.
The flat itself is cute and comfortable with a good kitchen if you like to buy locally (Mercato Centrale is 15 minutes walk but you can also pop into the little local shops and pick produce grown in Italy) and cook for yourself sometimes, which I highly recommend doing.