Hi John,
I think that the effectiveness of that device would depend as to weather it is designed to modify the pulse ratio from the drive shaft pickup so as to alter and possibly correct the speedo reading in any and all gears, and or, to also act as a rev. limiter,as driven from an ignition, or crank angle pulse, pick up, and consequently restrict the vehicles maximum revs. and therefore its maximum speed in any and all gears.
Perhaps the only option you have is to ask the pertinant question from the supplier.
Cheers, Winston66, Northampton , Western Australia