Hi..
I had a previous query - answered by David Smith here - http://www.gravityhelp.com/forums/topic/adding-hidden-fields-to-all-pricing-fields-output
But he didnt' come back to me with a more detailed reply on how to use the gform_product_info hook and your documentation is a little thin.
"append the hidden field to the product name when displaying the pricing table (and other places the products are aggregated) using the gform_product_info hook."
Any more examples of the hook in action?