The location of this apartment is fantastic. You're right near everything you'll want to see on your trip to Florence. About a 5 minute walk to the Accademia gallery, 5 minutes to the Mercato Centrale, 10 minutes to the Duomo, 10 minutes to Santa Maria Novella train station (nice if you're arriving via train as you won't need to take an expensive cab ride).
The apartment is clean and well-kept. Furnishings are basic, but hopefully you're not spending too much time here and are out experiencing the city. When you are there, there's a fantastic view of the Duomo's dome from the small terrace off the bedroom.
Be prepared for a climb with your luggage, the suite that the apartment is part of is on the 3rd floor, and the terrace apartment is up another flight of stairs from there. The door locks are also a bit tricky, it can take some jiggling and fiddling to find the sweet spot where they open. Neither of these things are serious defects, just something you should be aware of before booking.