I got the BSC Lock. It is just a high pressure ball valve. So that i can lock the rear or the front. If i press the brakes, then close the valve, then unlock the brakes the rear will stay locked so i can do a front dig. It i close the valve, then press the brakes i only send pressure to the front brakes and i can do a rear dig.
The Spidertrax one you would actually need 2. One for the front and one for the rear. It is made by Jamer and is actually cheeper that apidertrax. So anyway back to you needing 2. It only holds pressure, it resets when you hit the brakes again.
Both are manual operated
Pete