First of all: Excellent Maitre D'
The food, while better than average, and pretty excellent by comparison to 'the world', this is Tuscany: And this is where excellence is easily obtainable.
The Duck was pretty good, and well worth a try. Definatly worth a visit. But if I had to choose just one place in this area, it wouldnt be Bagni di Pisa. It would be Locanda Sant Agata (3km away), or just acorss the road 'Pasta e Vino. Both are just 'better' in every way (OK, Pasta e Vino doesnt have the 5 star service), but for food. Its definatly a Diamond, but it just doesnt out shine the Diamonds that Glint nearby.