Anyone find any actual material (printed or online) about the offer?
When you can only get the $10 coupon for buying $100 cards, sure, it's a nice way to get some 40% off groceries at an expensive supermarket, but, it's not a practical means of MS. When you get it on the $500 cards, it then becomes a 'bonus' on your regularly scheduled MS.
If the printed material has no exclusions on variable loads, or, doesn't say anything about 'must get exactly $100', then one has good great recourse when the coupon doesn't print if they have printed material about the promotion in hand.