Remember that the costs to calculate any savings needs to be compared not just to what you actually ate, but what you likely would have eaten if you'd not been on the plan at all. For instance, if you normally wouldn't have eaten/ordered dessert with every meal then there may be no "real" savings. Or if you would have ordered an appetizer rather than a dessert, which is NOT included in the DDP, then there may be no real savings.
For us, as two adults, we actually save $100 to $150 per trip paying out of pocket for our meals by ordering what we WANT to eat and enjoying it, rather than having dessert with every meal. And we do not scrimp.
Also ordering more expensive items simply because they are included does not reflect true savings.