Some of them are designed for such small pills, those might run a few more dollars. I worked in an inpatient pharmacy for awhile and we regularly cut tiny pills.
They are fairly ingenious for how simple they are, basically you put the pill in a V-shaped compartment so it would settle down to the base of the V. Flip the lid over and a razor blade would apply even pressure and split any size pill perfectly in half.
Some were more amenable than others to the splitting, while some would explode into a chalky mess, but I think that had more to do with the filler than the ingredients, which gives the opportunity to shop around.
