Technically, I'd say nothing. But in today's market, who wants it apart from the few weirdos that hang out here? 😀 99% of the market is perfectly comfortable with other forms of focus confirmation.
I want one.
And it is way cheaper than my Minolta Hi-Matic 9. I spent the whole Summer of 1969 mowing lawns to buy it. I would only have to mow 40 lawns to buy an X100, and I have a John Deere.