Checkout Buddy offers new checkout customizations based on Shopify’s new Checkout Extensibility features, specifically Checkout UI components, Functions, and Checkout Branding.
Functions like product discounts or payment method customizations are available to merchants on all Shopify plans, and do not require Shopify Plus
Checkout UI components (blocks) and checkout branding features require use of Shopify’s Checkout Editor that are currently restricted to merchants on the Shopify Plus plan only.
As long as these restrictions are in place, Checkout Buddy features related to blocks and checkout branding will require Shopify Plus to be used.
https://help.shopify.com/en/manual/checkout-settings/checkout-extensibility