From https://stripe.com/blog/stripe-checkout:
It’s unfortunate that everyone has to reinvent the wheel when the time comes to implement a payments UI. We decided to build something that you can just drop in as a single tag
The script tag creates a “buy” button on your page. Clicking the button pops a modal payment form where the customer submits their info directly to stripe. It’s a literally a 30 second integration. But here’s the kicker:
By integrating Stripe’s payment form, your checkout is continually improving. As we refine and iterate over time, we’ll be able to immediately pass enhancements on to anyone who uses it.
Yes, they transparently push you updated payment forms as they make changes. My first thought as a developer is “that’s asking for a LOT of trust”. But ultimately I think this is a perfect tradeoff between control and convenience. Asking for control over your payment form is crossing a line (now they’re interacting directly with your customers) but it isn’t far beyond trusting them with credit card numbers. And taking that trusting step enables one of the easiest integrations of ANY web service, blowing open the doors to the less-technical market.