We had a great time in Florence, and Donella's apartment was a huge part of that! It was clean, cozy, and had everything we needed - linens/towels/cookware/etc. The internet was a bit spotty at times, but worked well enough. Donella was terrific in communicating with us before and during our stay, and was gracious with us even though we got lost and showed up a bit late!
The apartment is about 25 minutes on foot from the Duomo and Galleria dell' Accademia, and only a bit further to the Uffizi and Ponte Vecchio. We didn't use public transit in the city, but it looked like it would have been pretty straightforward to get around via bus as well.
There is a cafe right next to the apartment, though it wasn't open consistently, and a good supermarket is only a eight minute walk down the street. There are several good restaurants within a few minutes walk - we particularly enjoyed I Templari.