Ever since I registered my Amex card with Apple Pay, I now receive instant notifications of all purchases on that card. This not only occurs for purchases using the NFC feature of the phone, but the notifications also appear when the card is swiped in the old way. One example: when a restaurant server takes my card away and swipes it, the charge notification instantly appears on my phone - before the server returns to the table with the card and charge slip. The phone was not used to make the charge -- the card was swiped in an old magnetic-swipe device. This notification is awesome, and is a great security feature.
Interestingly, this instant notification feature (for non-iPhone transactions) does not appear for two other cards that are registered on Apple Pay - only the Amex card has this feature.
This feature is so useful that It surprises me that Amex does not advertise it. Frankly, all cards should work this way. Wouldn't everyone want to know instantly whenever your credit card us used for a transaction?