EDIT: I see you have the 100% carnauba version of P21S. I wasn't aware that P21S sold two versions.
S100 would be a near carbon copy of the cheaper version of PS1S. So $15 vs. $38 vs. $60.
The only issue however with 100% carnauba is that it will degrade quickly with heat and moisture, unlike a synthetic wax but the wet look shine is obviously not as good as with the pure carnauaba. I guess it depends on how the car is used. One trick that can extend the life of either S100 or the two P21S versions is to apply a polymer spray over it once the wax has set up for a few hours (needs a cool ambient temp). Finishkare
#425 is probably one of the better 'last step product"s I've used. Bare carnauba wax can be a bit of a dust magnet. The #425 gives it a teflon like finish to the touch while preserving the shine. Dust rolls right off So less of a need to do quick touch ups. It has this same effect over synthetic waxes as well, convenient for when your car is parked outside as the wind and light rain fall will roll dirt off the paint. Once you slide your finger over it you'll see what I mean. I haven't seen this in many other products. So it's an interesting mix, something very natural like pure carnauba under something very 'advanced'. Mixing the two into one product does not seem to work, layering is required.