This was a POSITIVE experience for me.
PROS: Location was fantastic! The Duomo was literally right around the corner (the Baptisery, actually). Had a supermarket on the same street too, which was extremely useful. Whole apartment was clean, bed was low but solid and comfortable. Soundproof, apart from the Cathedral bells. Lots of tea/coffee/etc was provided. It really felt like a home in Florence. We really liked having the luggage room for the end of our stay, and Francesca had impeccable communication (one thing to note is she recommended the Firenze Card - probably super useful in high season, but not needed in January). Good heating.
CONS: The bathroom smelt unpleasantly funky, but we found this smell permeating a lot of Florence's buildings. An air freshener was provided so we cranked it up to high, which hid the smell for the most part. Stairs within the apartment are quite narrow, so may be a problem for people with balance issues. Downstairs area (dining/kitchen) was really small, but didn't matter too much as we did not spend a lot of time there.
OVERALL: We really liked Francesca's apartment, apart from the smell in the bathroom. I would stay here again for the amazing location.