This little beauty essentially allows customers to receive product offers right within checkout after they've entered their card details but before the thank you (order status) page. What's real neat about this is if they opt-in to the offer, they do not need to enter their payment details again (as is possible now using Order Edit API). This ladies & gents is true upselling that rocks aand is why this is such a BIG deal. You just had your customer buy something, you already have their card details, you peddle them another offer, a cool upsell that makes sense and has a good discount. One click is all it takes for them!