I was truly impressed with Mirella's place. It was pretty much exactly as I had expected, even a bit better, based on the photos and the earlier -- very flattering and accurate -- reviews.
The location was extremely convenient -- the place is right at the edge of the Arno, very close to Ponte Vecchio -- but on the non-touristy side of the river, so it was quite homey. There was a supermarket, several cafes, a gelato shop, and a great restaurant on the same street. Being so conveniently located there was some noise at night from passing traffic, but it did not extend into unearthly hours.
Everything else was wonderful -- the apartment is extremely clean and looks newly remodelled. The furnishings were tasteful and useful. I used the sofa bed downstairs, and found it very comfortable. The kitchenette was clean and well-equipped. There was even a laundry room.
Mirella was an extremely considerate host. She had thought of everything -- from clean towels for everyone considerately wrapped in tissue, clean sheets, hairdryer, even bottled water and snacks for hungry travellers, bags for trash, etc. She responded quickly to all questions, took us around the place, showing where the light switches were, and even reserved a taxi for us to go to the train station early in the morning.
I would definitely try to stay at Mirella's if I were to visit Firenze again!