G'day mate, I put a TZR50 cdi on my '07 ZX and it runs fine. My cdi was starting ok when cold, but when warm, if you stopped for 10-20 minutes it wouod be a bitch to restart. The TZR50 cdi is supposed to be a race cdi, I don't know if that true but it does have no rev limiter. I have got a thread on it in the general section titled ZX50 CDI. In that thread I have listed the wiring so you know which wire on the cdi goe to which wire on the scoot harness. I bought the Honda Dio CDI as it was $10, the ZX50 one was $64, the only difference was the plugs. For what it is worth, I now have easy starting.
good luck and welcome to the forum, stick around awhile and you will learn a lot about these scooters.