Turbo heads are better for on-road. The plugs are more sensitive to vibration and dirt so in off-road where the plugs gets beaten by the vibration and jumps and bumps the could fail more often. Also since they increase top end performance, most of the time they won't help.
If you're just fooling around in the street and want a little extra power up top it might me a good idea. For off-road I've always had better luck with regular plugs.
Velocity RC Magazine