The Honda S2000 uses VSS for the oem cluster, ecu, soft top module, abs, and electric steering. All the wiring is there stock, so why not just tap directly into it and feed everything with one signal that you can calibrate for any factor such as; tire size and final drive. Taking it off the tail shaft ensures that you can’t have a difference in wheel speed side to side. This is why stock it’s taken off the trans. Second by keeping everything near the tail shaft you drastically reduce the amount of wiring you need to do and time spent. If you just use one rear wheel and input that to the ECU you will then need to have the ecu output that signal back to the rest of the car using up an output.