In your first example it is clean, readable and perfectly fine to use it in that way.
In your comparison of C# and VB both are perfectly understandable to any developer of almost any modern programming language.
The ternary is familiar to any moderately experienced developer. In the examples in your article they do not in any way improve upon the standard if statement or aid in functional programming.
The norm is to use if..else if..else for multiple clauses. Deviating from that norm needs a good reason. The examples in your article are not good reasons.
The reasons being that when you start to substitute statements and blocks with expressions, your code will be much easier to write functionally. It it hard to see the benefit from just this one article, but it's an important (small) step towards creating functional (or pre-functional) code.
The same arguments could be said about a for loop or switch statement, which like if are also imperative (non-functional) constructs.
I also remove for and switch for more functional code.
Replacing a single if else statement with the ternary operator in a lambda function does enable you to write the logic in one terse expression on one line. I agree that this is a good thing.
This does not make the ternary operator functional and the if...else block not. It's just a, in this use case, more appropriate syntax for exactly the same result.
You could rewrite a single line arrow function that uses a ternary operator as a multiline arrow function using if..else and the function would still be functional, it would behave in exactly the same way.
The ternary operator is great for a single one line piece of logic. It is less great for multiple if..else if logic - just use an if block, it's easier.
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