First: location, location, location. You are 2 minutes from Ponte Vecchio, which puts you within striking distance of most attractions. BUT you are on the less-touristy side of the Arno, with way better restaurants. And cafes that don't jack up the prices. The Oltrarno is definitely the place to stay. Piazza Spirito's weekly markets are well worth it. Did I mention the better restaurants?
The apartment: this isn't one of those AirBnBs which has had all personality, personal effects removed. Because Martina still uses the apartment, it has her personality all over it: think bohemian, artistic, intellectual. The apt. also gets plenty of sunlight (unusual for Florentine apts.) except for the bedroom (just as I like it). As others mentioned, even in winter you can have a mosquito issue: just don't sleep with the window open and you'll be fine.
This place is so much more than any hotel room, and certainly beats just about any AirBnB in the area. And Martina! She is truly a gem. The place was a little more expensive than I had budgeted for but was worth it.
My one word of caution: not a great place if you have any mobility issues. Very steep stairs, tall bathtub, etc.