I stayed in this apartment with my family of eight while we were in Florence and we had a fabulous time!
This apartment was in a beautiful location, close to the train station and the Duomo, and a short walk from the Uffizi gallery and Ponte Vecchio.
We found it to be safe and very clean, with good security features like a gate downstairs and deadbolts in the door.
The hosts were very nice, gregarious and helpful; Rino even met us at the train station and brought us to the apartment.
We found it to be a plus that there were lots of keys available upon request.
Everything was ready for us when we arrived: towels (and extra towels), sheets, fully stocked kitchens, etc.
There were also fans in every room, which was a plus for summer time, and mosquito nets so we could keep the windows open.
The wifi worked well--there are actually two routers since the apartment is quite large, so you can get signal everywhere.
Overall I would definitely recommend for large groups looking to stay in Florence :)