I really never thought of using a hand-held unit. I have a Garmin gps ll and a Magellan 2000. Wonder if either of those would work.
Actually, the motive is to have a tach and speedo close enough together that you could possibly catch any wheel spin. If known by calculation, a given rpm = a given speed. If the tach reading increses without the speedo increasing, time to back off enough to get traction again.