If you go to the manufacturers web sights they will explain the purposes of each of their lines of products and their purposes. A composite designed for a deck does not have the same density as a composite designed for a structural transom. Transoms will have much more pressure put on it from the through transom bolts that hold the motor / motors / bracket and the pressure put on it from running in seas and trailring it that what a 200 Pounder walking on the deck would.
FellowShip
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My motto: Just for the Grins