Recommend scanner for Gen 1 Prius (2002)

What kind of scanner would you recommend for my car and how much can I expect to save with it in gasoline? I currently get about 60 MPG if I drive long distance (highway). What gauges would I benefit from and what would they show?

Note that I already have a laptop that can connect via OBD-II and read/clear codes as well as read some vehicle parameters, like fuel trim, throttle position, MAF sensor, MAP sensor, etc, so this would not be very beneficial for me.