If prime location is of utmost importance in Florence I can't see how you could do much better than Silvia's apartment. We were less than 10 minutes walking from the Duomo, Uffizi, Palazzo Vecchio. And less than 20 minutes walking from the Boboli Gardens. The view from the living room I quite liked and there is an abundance of natural light to enjoy!
Other reviews have commented on the stairs and we can confirm there are a fair amount. Definitely take this into consideration if you don't do well with stairs or can't carry heavy luggage as there is no lift to the top.
I will also confirm that the current bed and pillows were quite firm and it felt like this did have an effect on my sleep quality. This combined with a few mosquitoes buzzing around and biting me in my sleep.
I do realize the bugs come with the territory but still worth mentioning especially as we stayed here in early April. The ceiling in the bedroom is very low and we did hit our heads a couple times but thankfully the wooden beam was padded. I'm 5'9 and could not stand up all the way in the loft. Just mentioning this to all the tall folks out there!
I read an earlier review complaining about noise but other than church bells (hard to escape in any historic Italian town) and occasional police sirens I actually found the apartment to be very quiet despite it's central location.
Silvia was very receptive and helpful to all of our questions and responded promptly to messages over the Airbnb app. His friend that met us at the apartment was very helpful in getting our bags to the top of the stairs but was brief in his explanation of how everything functioned in the apartment. I think a handout located somewhere would have been helpful just for the things I could not remember (example being the air conditioning unit).
All in all, we had a pleasant stay at Silvias. Again, if location and walkability in florence is your prime criteria I'd say it would be hard to beat this apartment for the money as long as you're okay with the concerns I mentioned above.