Yeah, my point is there are much better options that would also induce fear and actually be effective. Fentanyl strapped to an explosive, or any of a ton of other chemical agents. Iran would do far more damage -- and create a deep source of fear that would likely have lingering consequences for decades -- by giving their HEU away rather than making an ineffective dirty bomb. There is no way anybody who knows what they had would use it that way. Even the most fanatical member of the Iranian regime understands what to do with the material better than that.

While true, the problem is it wouldn't meaningfully change the security situation for Iran.

Deliverable nuclear weapons make you invasion proof - nobody wants to risk it. A "dirty bomb" isn't something that can come flying in on an ICBM and eliminate large chunks of your nation - the threat of it is more likely to enhance aggression rather then deter it.