You really don't have a need for a
trans brake unless you have a stall converter and spend a lot of time at the track due to the expense. A
trans brake allows you to rev the engine to the stall speed on the torque converter so that when you release it the vehicle takes off rather than waiting for the revs to build. It's good for an advantage on your take off in bracket events. It uses a solenoid in the valve body to lock 1st and rev with fluid pressure so the vehicle doesn't roll through the beams while allowing you to rev the engine (almost like holding the clutch on a manual only the vehicle won't roll).