I can understand how that could be confusing, I'll work on the messaging in-game~ essentially the unlock is supposed to be the primary way to create another option to consider when retiring heroes (making them into an item vs. using them in the eternal strife, or turning them back into gold). while the item is an alternative way to get those items without having to retire your best heroes. The item currently shortcuts the unlock and allows you to do it much earlier than intended, but is also fairly rare.
I'll take the idea back to the drawing board to try to make it make more sense because I do agree there is some disconnect there, and I don't want players retiring heroes and thinking they'll have access to them in the Beyond.