You get the 5% cashback on Amazon.com purchases. That would appear to be the real value-add here, because you would also get that cashback reward using the non-secured and well-established Amazon.com credit card.
I see it as just another ploy to get you to spend more money in the Amazon ecosystem.
2-3 years ago, I was making a purchase on Amazon at least once a month. These days I only use Amazon for price-matching at other stores.