Yeah, there's no benefit to this if you have any of the fee Delta AmEx cards. The 20% rebate means that 8 $9-priced drinks only cost $57.60, and Main Cabin 1 boarding is already included. That means that it costs $1.40 more for the brag tag versus buying the drinks outright on the Delta AmEx card.

It might make sense for those who either can't/don't want to get one of the fee AmEx cards but still want MC1 boarding, or those with the Blue Card that don't value checked bags enough to pay the fee but could justify the drink cost plus the extra $1.40 (assuming all drink coupons are used) for MC1 boarding. I'm wondering how big of a group that is. That said, $59 for the drinks plus some other benefit not on the AmEx cards (maybe a couple of SkyClub passes?) could tip the scale.