An update on my 529 research although it's a bit OT: yes, Iowa's plan looks good but the only way for DS and DDIL to get the tax benefit (they're IA residents, I'm not) is for them to own the accounts, meaning that they'll count against any needs-based financial aid the kids could get. They'd get maybe $1,200 state tax reduction for $20,000 in contributions (husband and wife limited to about $10K contribution each). That means if I gift them anything more than $10K over and above that I have to start reporting it for estate tax purposes.
BUT...Fidelity has access to a Massachusetts plan open to non-residents that offers ETFs. Going forward I'll leave what I have with Eddie, deposit the max I can deduct off my MO taxes to EJ ($8K in 2021, I think) and the rest will go into the Fidelity account, which I will own.
Thanks for making me think. The oldest is 7 so I have plenty of years to reap the benefits of lower expenses.