TY!~
The good about zero frets is that you get easy production with controlled string elevation. A spacer goes behind the zero fret, and this can be made variable if desired. Tone... I'm not sure just how much its effected. In production, you also have nice breakaway for the strings, so they tend to be buzz free at "the nut". Tuning woes, strings sticking in the slot, are gone.
The bad is - they wear out, get ruts and grooves fairly rapidly. A really really hard zero fret - hard stainless, might be interesting, but for all these years, a regular string nut has done everyone pretty well.