The human body can't absorb iron from iron oxide. It is insoluble in water. Iron in the lungs is at the very least just as bad as any other fine particulate.
I mean I didn't go super deep into it but from what studies I could find on iron oxide absorption / adverse effects (that were admittedly performed on non-human animals, but the results should still be applicable in this case) there was in fact absorption of iron, it just wasn't much.
Regardless, the broader point I was making in the comment was more so about how it's not inherently toxic or anything, and the concerns about the rusty screwdriver chewing come from contaminants or fine particles getting into the lungs, not about using rust as an iron supplement.
On the last point fair enough, I recognize its not like its uniquely dangerous, but I feel it's still a relevant concern given the users behavior. I can really yap when explaining things so I mostly was trying to keep it concise rather than really explain the fine details and get into the nitty gritty of it.
