There is some controversy where some owners are saying on steep hills and for stopping they use the parking brake.
The treadle pedal should control speed, including braking. For steep hills or heavier loads it is wise to use 4x4 and the differential lock for maximum stopping power, by the HST. The parking brake can not do more, but is often the go-to when someone panics.
Pressing gently on the reverse pedal will slow and stop the BX before it goes into reverse. That pedal also has an ignored grease nipple that reduces friction so the pedal will center itself.
The parking brake is actually a transmission lock, and the brake discs are inside the HST case, so it would cost a couple thousand dollars to replace.