To answer your question, is a centax needed,,, no it isn't needed.
But if you're the type that travels and races at several different tracks then a centax would be helpful. Or if you're the type that likes to make changes on your car just the heck of it, a centax is fun to have.
As for the NTC3, adjusting a centax isn't that hard. Maybe it is easier on a belt driven car where the clutch is more exposed but still,,, you won't have to take the engine and clutch off to do any adjusting.