> But I'd be very skeptical of putting a one-liner from a generator into my DNS without understanding, at least at a basic level, _what_ it was doing

You're completely right, of course. In my experience, these generators usually explain what the generated code means, though. These records are a lot easier to read than they are to write if all you've got is a manual and a technical specification.

I haven't used any hosted mailing services myself, but I can't imagine their control panels don't have either an option to generate the necessarily policies for you or an extensive guide on how you should configure these records and why. These records are the only part of the mail ecosystem these hosted platforms can't manage (unless you also let them do DNS) so they're a crucial step of the onboarding process.