Yeah, I looked into it, too. I think it's worthless since you can't combine the discount with other discounts. They should make the deal more attractive.
The best credit card out there is offered by PenFed, their Platinum Rewards Card that gives you 5 points for gas and 3 for groceries, which translates into 5% and 3% back. 1% for all else. I don't know of any other card that give you more for gas or groceries.
No annual fee and great rates as well. Customer service is fantastic. It's a credit union, so you just need to open an account with $5 and then you're in. You don't need to be a federal employee or anything. https://www.penfed.org/Platinum-Rewards/