The adjustable discharge baffle operates inside the deck, while the OCDC kit operates outside the deck.
The adjustable discharge baffle doesn't actually block the discharge opening at all. When the baffle is fully open, it allows clippings from the left-hand side of the deck to partially bypass the center and right-hand cutting chambers. The primary benefit is that the cutting deck requires less power in this configuration, allowing for higher ground speeds in heavy cutting conditions. There is some impact to clipping discharge, in the sense that the discharge velocity is not as high when the baffle is fully open. When this baffle is moved to the "closed" position, the distance between the blade tips and the baffle decreases. As a result, the clippings tend to be cut into smaller pieces, and the discharge velocity increases (because essentially the same amount of air is being pushed through a smaller opening). In some conditions, this will result in clippings being thrown farther from the deck. However, in other conditions (especially drier, less dense grass) the higher velocity will actually cause the clippings to scatter more (and disappear more).
In contrast, the OCDC can be used to block off the discharge opening. The accessory has three positions: open, closed, and an intermediate setting. In the open position, grass discharges from the cutting deck just as it would without the OCDC kit installed. In the closed position, a rubber paddle blocks the discharge opening in order to prevent clippings from being thrown out of the deck. (The paddle does not form a tight seal, so the deck is allowed to breathe, avoiding the potential to create a stream of pureed clippings along the edge of the deck.) In the intermediate position, clippings are allowed to escape from the deck, but the throw distance of the clippings is reduced.
-The Toro Company