This is what the information representative had to say when I inquired about the Legacy/Impreza gear kit:
The gearkit sells for $3,875. Synchromesh refers to the type of gear
engagement. All street cars have synchromesh gearboxes due to their quiet
operation and ease of use. Race cars use dog engagement which do not use
synchronizer rings. This form is much noiser (not suitable for street use)
but has the advantage of greater strength as well as not having to use the
clutch to upshift.