Some models offer an open universal fork pockets, while others have tubes sized and located for specific order selectors.
The more open universal approach offers flexibility in mixed fleet applications. These mostly designated as carts, as they work best in applications where the cart is filled and dropped for another cart like
Specifically designed fork tube models are made to fit a specific truck. The deck is less likely to skew since the horizontal deck is locked in by the fork tubes and the wood clamp block.
Note there are additional differences and a review of your application will uncover the trade offs.