Remember that most of the time, either a CTx4, or CTx5 will hit almost everybody on the field. Math skill is great if you know what you're doing because there is no charge time, and does not cost Mp.

It does take a bit of work to do the math but it can be very powerful as there is no range to a math "spell" so you can hit nearly every enemy with a Holy or Flare or your entire party with a Cure 4 or Haste.
Calculators can't cast Cure 4.