Does anyone here use American Express “Global Diner Access” program?

Hey everyone. I'm seeing this icon next to many of the restaurants I'm interested in on Resy and I'm wondering if I should get an AmEx card. Could anyone here tell me:

How does the "GDA" program work?
Is it worth the hassle of getting an AmEx card?
Are you actually able to get a reservation at (for example) Semma using it?

Thanks!