That’s mostly true, though I differ with you on iron gall inks. Some are really quite lovely with a fountain pen, but one must make sure one is using an ink that is formulated for a fountain pen. That said, I usually use them with pens that have converters in them, rather than vacuum fillers or the like, because of the cleaning issue. In fact, I usually dedicate one pen to such inks, so it saves time on cleaning up.

Perhaps more importantly, only Noodlers seems to make inks that will work as “security inks”. All the others I’ve played with can be taken off one way or another.