Marco's studio was perfect for the two of us, and our host couldn't have been more welcoming or helpful. It is compact but with all you need for a short stay in Florence. We were out sightseeing during the day so mainly used it as somewhere to sleep and have breakfast each day. We did cook for ourselves one evening and the facilities were fine.
The area is quiet and away from the main attractions, although San Niccolo has its own things to see and do, including Piazzale Michelangelo and the view over the city at sunset. As first time visitors to Florence, we appreciated being able to walk into the city, across Ponte Vecchio, for example, and so experience approaching it from a distance with tantalising glimpses of the Palazzo Vecchio and Duomo. That said, the walk to Pte Vecchio takes less than 10 minutes. (It's also very handy for the no. 23 bus to and from Santa Maria Novella train station.)
It was nice to come back to a quieter part of town at the end of the day. San Niccolo has a lovely atmosphere and plenty of amenities (bakeries, convenience stores, launderette) as well as a good choice of bars and restaurants which seemed as popular with locals as with tourists.
Florence was all we hoped it would be, and more. Staying at Marco's studio made our visit that extra bit special.