You'd also know that they're advertising that they're open to being approached - it might relieve some anxiety knowing that you're going to be rejected simply for approaching someone that isn't interested in being approached at all.
>just put the digital equivalent of "hey ladies I'm single" and wait for the women to swarm? Yeah, ok.
Yes, they've gender-inverted their example in order to be politically correct. You're right that men will still pursue, but I think the app might offer something to men who are less than perfect at detecting which women are signalling they want to be approached. A lot of men would like some de-risking on that front, even at the expense of reducing the total size of the pool.
EDIT: wait, unless it's a thing like bumble where only the woman can make the first move? In that case yeah, I don't see it taking off