This place is better than "Average" - "Good" would be the rating, if they had it. There's nothing fancy about this B&B but it is 5 minutes from the train station and 20-25 minutes from the Tower (there are a few other things, but not much more to see in Pisa). There's even a few of the Tower if you look off in the distance from the balcony.
The rooms are simple - some with ensuite bathrooms. The showers are typical Italian-accommodation-tiny. The beds aren't super-comfortable but certainly sleepable. Maria, the very friendly and helpful owner doesn't speak much English (Italian and French instead) but her staff generally does.
It is best to give them a call before you arrive. IGNORE the Google mapping of this place it is wrong. It is on Piazza Sant'Antonio - walk straight out of the train station to the end of that big street. At the roundabout veer left. That's the Piazza. Google maps will put you at the end of Via Sant'Antonio which is by the river and will make you waste your time.
You probably won't stay more than a night in Pisa. This a good place to spend it.