First off, I want you to know that I lead Developer Relations at Fast. I thought you should have that context so you can decide how this review affects your decision.
Fast increases conversion, boosts sales and delights customers.
Once a seller purchases from a Fast store, their private data is stored in their Fast account. The next time they visit your store—and many others across the internet—they'll be able to checkout in seconds. I personally see it like 1password on steroids, a way to safety store my payment and shipping information for me to leverage quickly—seconds in this case—when I'm shopping online. I can't wait until subscription companies start leveraging Fast too.