It's basically begging for you to switch apps after you get the "Yo" push notification. I can't really imagine a conversation which goes like this:
Me: Yo
Them: Yo
Me: Yo
Them: Yo
...
What I can imagine is getting a Yo from someone, switching apps, and being like "what's up? [p.s. dont fucking Yo me anymore. Just message me using a real app.]".
That "wut" app is similar in that you can't have a real conversation with anyone in particular, but it can at least be used for sharing secrets or something. I guess. Yo doesn't have such a use case that I can see.
They could maybe pivot it to act like tinder where if both of the parties yo eachother then it goes to a separate section of the app where they can actually IM eachother. But...idk. That doesn't seem particularly interesting/differentiating either.
I must be naive/short sighted.