I just tested out a pair of trackballs. Both are Happs, but one has the Electric Ice upgrade kit (sans lighting at the moment) and the other a standard white 3" ball. The regular ball has slightly more heft and spins a little cleaner, plus it feels smooth. On the other hand, the EI lights up, and the differences are neglible.
Yes, my tests were hasty and very unscientific, but as such, I haven't any qualms with the Electric Ice upgrade kit.