Stripe checkout is as easy to integrate & also well designed. Why bother to have yet another middleman in the game.
Stripe Checkout requires that you know how to write and integrate code. Plasso does not. Of the 2.4 billion people with internet-connected computers, only 1-2 million can write code.
Here's the Stripe Checkout integration guide for Rails for example: https://stripe.com/docs/checkout/guides/rails
Clicking "Learn More" links, in many places, literally takes you to api documentation.