We have staying at Bettina's studio for 2 nights during September 2011.
What a great place to stay!
The location - a few steps from the wonderful Michelangelo's David statue. go to the other side of the street and you'll hit the beautiful Duomo of Firenze. 10 minutes walk to the train station. there's just no better location in the city.
The apartment - very clean and spacious, cozy and well designed. you'll find everything you need and more including full kitchen, wide desk, and even a washing machine that was really handy. The bed is comfortable and the balcony is a great bonus.
The host - Bettina was a wonderful host. She came to pick us up from the car-rental, made sure everything is alright during our stay and filled the kitchen with good-to-have stuff.
Bottom line - don't think twice and go for it! You will enjoy!