I'm not sure what you're referring to - do you mean a chip that modifies the fuel injection process? Quite a few people have done this mod, search for "chip" (without the quotes) to find threads about their experiences.
I'd say overall:
* You get more power at the cost of more fuel
* You can get better economy by using that power wisely
* Chips void the Nissan engine warranty so don't let Nissan catch you with one in the car
Is it worth the $ spent? I think that's a decision you have to make for yourself, but please do that search and read about other peoples' experiences.