Because allen the nelson tune guy can go in with a computer and change the settings in your computer to exactly what will work best for the way you drive and the way your vehicle is setup. The jet stuff and the handhelds are "one size fits all" type deals, they offer some improvement over stock, but they can't change near as much to your needs as a nelson, and thus can't give you near the gains. Once a nelson tune becomes available for my truck, i'll be all over it.2kSub said:why is it so great over a jet stage II? Also, why the comment about "stay away from handhelds"? I assume you mean something like a hypertech?