Our stay here was great. Communication was good from the start, and we got in to our unit easily. There is a lot of security, so that made us feel very safe, although you will need to open three different doors with either the keys or the pin code (1: building door, 2: upstairs door to the top floor, 3: door to the patio that is exclusively for this unit, 4: (optional) door from the patio into the unit, which we left unlocked because we figured 3 locks was enough).
The apartment was comfortable and well-equipped. The AC (air conditioning) worked well, although it does not send air directly to the upstairs bedroom area. This was mitigated by the powerful fan that you could use upstairs, which also might help if there is any street noise (we did not notice any, but the fan might have drowned it out). The fan and AC had remotes so you could control them from bed. The bed is comfortable, although there is no comforter (just sheets). It was fine since the room was cool but not cold (we ran the AC at night because it was quite hot in Florence at this time). Wifi worked well - no issues there.
The location is SUPERB. It's about a 2 minute walk to the Duomo, in the heart of the historical city center, and you can see both the dome and the bell tower from the window. This is, by itself, a great reason to stay here.
There are definitely some significant caveats to consider personally, although none of them bothered us:
1) There is no elevator/lift, so you will need to be fine taking the stairs to the 4th floor. Exercise is good!
2) Water pressure is good in the sinks, but quite low in the shower. This is par for the course in Italy, from my experience, and to be expected when you're staying in a historic building in a location like this.
3) The bathroom is quite small - although the shower is spacious by European standards.
4) There is a narrow spiral staircase leading up to the bedroom area/loft. It's quite narrow and steep - not a problem for us - although if you have mobility issues, especially getting up at night to use the bathroom downstairs, you might want to avoid it.
We knew all of this going on, were fine with it, and were not bothered by it, so our stay was great!