Great choice if you're looking for accommodation in Firenze! It's located in Oltrarno (other side of the Arno river from the tourist attractions), which for me is a plus. It's still only a 20 min walk to main attractions and it's so nice to take a break from the crowds of tourists. Piazza Santo Spirito has been one of my favorites ever since I studied abroad in Florence a few years ago, and it's only a 5 minute walk away from the apartment.
You do have to pay a tourist tax of €2,50 per person per night stay in cash when you arrive, so keep that in mind. The shower was a bit moldy, but nothing too crazy. The street is quiet but can get a bit lively with all the cars, buses, and bikes driving by during the day; but you should be out exploring during that time anyway :)
I didn't get to meet Irma, but the lady that she sent to check us in was lovely and helpful. I would definitely recommend Irma's flat!