Sure, there's a solid argument that red flag laws have a 1) a lot more due process than no fly lists and 2) enough due process to make them constitutional. As I said, I don't know the details of the different red flag laws, and haven't formed an opinion on that.

But the comment I was replying to made a very different and I think highly indefensible argument: That the difference between red flag laws and no fly lists was the former was more effective.