Just got my watch (fastest delivery ever - FedEx shipping notification this afternoon at 2:20pm, delivered at 2:33pm). Will try out Google Pay later - I was a little thrown off when it indicated I actually had to call Amex to have them authenticate it (never had to do that with Google Pay/Wallet in the past - was always by a code), and especially annoyed by the same being required with my bank who says it might be done in 24 hours, but my confidence level on that call is low.
Either way, Amex is my principal payment so will be very pleased if that works.
Edit - tried it at the local grocer, worked fine. It'll be nice to be able to not stress if I leave my phone behind, in the car, etc, whether intentionally or not.