Custom barrels that have chambers cut for the purpose you have in mind, and are fitted to the individual gun usually produce better accuracy.
Drop-in custom barrels with too-tight chambers for the trash ammunition being used gain nothing in accuracy and lose a lot in reliability.
Unless you can consistently shoot under 4" at 25yd with your MP, I'd spend the money on ammunition and lessons, not a Storm Lake barrel.
In othre words, a custom-fit barrel for a specific purpose is often worth it. Installing a drop-in just because somebody said it's neat is often a waste of money and sometimes a headache. I see them on the range, and can track their location by the cussing.
