Lazer ZX-5 SP or FS ?

[AndyCandy]

Hi to everyone I'm new here, but I would appreciate if someone gave me an advice.

I have a Lazer ZX-5 KIT buggy, but I'm not happy with its performance on track and I would like to upgrade to SP version.

However, FS upgrade is available now and I don't know what to do...
Has anyone already used FS upgrade kit ? Which upgrade is better: SP or FS ?

Thanks for all answers.