As the op says - is a "logic-variant of Null"
No, it's not.
> Or a "typed null" to be more precise.
To the extent this is true, it is a fundamental difference.
> It's got some nice properties, but really it's the good old tri-state.
No, it's not. Because the Boolean type contains only True and False, not Null and the Option<Boolean> type (likewise, Option<Option<Boolean>>, etc.) does not contain True or False. There's no weirdness in doing logic operations on an Option<Boolean>, or a pair of them, because it is a type error to attempt it because Option<Boolean> is not Boolean.
I agree that for other reasons it's better, but conceptually they are used to represent the same thing. (Logic variant of null)
Yes it is, the point they make is that Option<Boolean> is explicitly tri-state in contrast to regular Boolean which should be two-state.
void f(char *x) {g(&x); printf(x);}
It's possible that calling g(&x) might cause x to no longer be null, even if x originally was null. It would then be inappropriate for the compiler to complain that the next instruction attempts to use x without checking whether x is null.
On the contrary it’s perfectly avoidable. You just need to use an option type with a language that supports comprehensive pattern matching and won’t even compile if you don’t explicitly consider the case of a missing value. If your model is flawed and you don’t want to explicitly specify that some value is optional then the problem is in your way of thinking. And there is no need to invent a language that doesn’t support nulls, they already exist.