We (a group of five friends) have stayed in Borgo San Frediano for eight nights, and overall our experience was excellent! The location is perfect if you want to go sightseeing in Florence and it is relatively close to the train station as well.
The host Marco is always willing to advise on nice places to eat and/or drink. Furthermore, the house is very clean and all the furniture looked great (including TVs in every room, separate bathrooms and plenty of cooking machinery :)).
You will not regret staying at Borgo San Frediano!!