To summarize, Buy 5 items in total of Item 1 and/or Item 2, then you get 1 free Item 2.
However, the free one does not get automatically added on the cart. For example if a buyer adds 5 items of item 1 in the cart, the free item will not reflect. The buyer will need to add item 2 once in the cart for it to reflect as free. Same thing happens when a buyer adds 5 items of item 2 on the cart, the free one will not reflect until the buyer will add another one item of item 2 to the cart then it will be reflected as free (with the price at 0).
It is sort of become buy 6 and get the last 1 FREE, which does not make sense.