The limited-time promotion is good at participating locations in the US and can be applied to any Footlong (with the free sub being of equal or lesser value) but is limited to one use per order. Extras (like double meat) are not included in the deal.
The way it works when ordering is: you add two Footlongs to your cart and the discount automatically applies if the location you select is participating in the deal.
Photo via Subway.
