I'm not clear what you mean about sites "using API" vs. "using only the simple redirect with email address and no API"?
For sites using PayPal Pro, the buyer has a choice of two buttons in their cart:
- The "Pay with Credit Card" button takes them to a secure checkout page where they provide their card account info to pay the merchant directly from the buyer's card account.
- The "Checkout with PayPal" button takes them to PayPal's site for a regular PayPal account-based payment, aka "PayPal Express Checkout"; in this case, PayPal would not offer the no-account card-checkout option on their site, because that's what the "Pay with Credit Card" option in the cart is for.
For sites using only regular PayPal Standard/Business/Premier, then PayPal would offer the no-account card-checkout option on their site if they don't detect a previous PayPal-login cookie in the buyer's browser. For instance, clear your cookies and test our PayPal demo cart with a PayPal checkout (you don't have to actually complete checkout, just see what options come up when you go there):