To start, the new button is available on the Cinemark, Movember and Rakuten websites, but you'll find it on BassPro, JoAnn Fabric, Papa John's, Saks Fifth Avenue, SHOP.com and Tickets.com by the end of the year. It should become more ubiquitous in 2020.
The credit card companies hope to create a consistent, simple user experience (with strong payment info protections) for all sites and cards. Users won't have to create or log in to an account to make a purchase. And they won't have to enter their card info into every new site.
This summer, we learned that Visa Checkout is shutting down in 2020. That wasn't entirely surprising, and given that Visa is part of the team launching this new payment button, it makes a lot of sense.