I have not used it, I do not calculate my own, I am lazy and just use emulsification systems.
I will say that susan barclay-nicols sells some of her books through lotioncrafters, and she absolutely knows her stuff. I consider her something of an authority.
I will also say that my confidence in Jen at Lotion Crafters is absolute. She knows her products and stands behind each and every one of them.
If I were in the market for such a calculator that is without question the one I would use.
JM2C
p.s. If you do try it please let us know what you think. Someday I may get ambitious and do the math myself.