Using a modal keeps the user in the context of the page they were just on, giving them greater control, which builds trust and reduces drop-off. This is further emphasizes by the desktop experience which highlights key item information on the overlay.

The directional experience uses two buttons, defining a single choice, minimizing cognitive load. The buttons are even stacked and have different colors to make them easier to distinguish.

The directional model lets the user pick how they make their purchase, so no matter what they choose their expectations are being met. It gets the right user to the right experience.

By moving the registration pathway after a purchase, we are supporting the user's primary objective, defining a more delightful experience, and then using the purchase as an incentive to register with just a password.