Calling “0.999… = 1” very unintuitive is a very strange thing to say, because that makes perfect sense to most children. I’d like to see a result that truly is unintuitive, like what we get with the axiom of choice.
Gotta call bullshit on that. First I don't think you have any robust empirical data on that question.
Second what's convincing to children that don't have enough knowledge of math to have formed any intuitions about it is not a compelling argument.
Except that's wrong, not all lengths do have a length between them.