I don't see how it solves a bigger problem: no use cases. Paypal started out trying to make it easier for people to give each other money. That foundered, so they pivoted into a commercial payment tool. It's like Square is reenacting the Paypal timeline backwards.
I haven't used Squarecash so not sure how it solves the problem of phishing. Reciving an email, clicking a link and typing in my credit card / bank details. Are we just expected to trust Square?