Their power user controls seemed to have a bit more power (at a reasonable cost) compared to the others I compared (mainly Fastmail), particularly in terms of number of domains. I have Calendar and Drive accounts in both Outlook and iCloud (and also personal Gmail), so an email-only/email-focused provider seemed an appropriate choice for this particular migration as I had already minimized my usage of GSuite/Google Workspace down to just email.
It's possible I'll eventually move on from Migadu due to this, even though there is otherwise a lot to love about the service.
In my particular case, a strong spam filter currently seems desirable. I've (tried to) train spam filters in the past and that's one of the few reasons I was still relying on Google Workspaces up until recently was as one piece in a rube goldberg "megaprovider" spam filter.
Though from what I see most of what Migadu is providing that cannot be turned off (SPF, DKIM, etc) are today considered best practices that you should add even if you were self-hosting, and the spam they prevent should be off your filters radar anyway, leaving your filter to better train on documents that aren't so bottom-of-barrel. (They are also, to my knowledge best practices to implement if you don't want to be entirely black-holed by the "megaproviders" as a self-host.)
I'm actively playing with this stuff so probably my requirements are a bit special, but even aside from that, it does still feel quite irksome that all mail input can't be cleanly recorded.