I like Mother's Sealer Glaze and their cleaner wax as well, but as far as the Pure Carnuba being an alternative to S100... Its not even close! I would rank the pure Carnuba as being slightly better than the MeGuiars Consumer waxes with a reasonable gloss and ease of removal, but S100 is soooooo much better in every way that its well worth the extra $$
And you can get away with using such a small amount of S100 that the price difference isn't as much as you think.
Just my opinion, but remember I am a big Mother's fan.
I'm a Mother's fan as well...and might very well choose Pure carnauba over Meguiar's #26 (although #26 is one hell of a good wax). In fact, I'll be generous and say that it would give Blitz Wax a run for its money.....but Pure Carnauba is certainly not in the same league as P21S Carnauba.