Changing name of duplicated sub-menu

I’m using this method
( https://developer.www.ads-software.com/reference/functions/add_submenu_page/#div-comment-446 )
by codex to rename the duplicated/first sub-menu of the parent add_menu_page().

My question is should I put the callback function on add_menu_page() or add_submenu_page() or both?

I’ve tested putting the callback function on one of them or both, and they work.

But I want to know which method is better in terms of performance and for avoiding duplicated data purposes.