529 plans are similar to a non-deductible IRA that is Missouri State tax advantaged. Put money for your kids tuition, get a Missouri state tax deduction, and it grows tax deferred. Any increase in value will be taxed if not used for qualified education expenses when funds are distributed, but if used for education the growth is all tax free. The maximum annual deduction is $8,000 if your single or $16,000 for married couple and you get a 6% MO tax benefit on your contributions (up to the maximum) in the year of contribution. That's a 6% ROR even if you put it in on Monday and spend it on the beneficiary's tuition h check clears!
Any 529 plan qualifies for the MO deduction, so you are not tied to Missouri MOST.