Discount Chooser simplifies the process of creating discounts based on items in the cart. You can create buy one, get one at a discount, buy two get one at a discount, or buy get a choice of at a discount. Item specification may be done by category or by product.
If you want offers involving more than just two items, Discount Chooser is a better option for your OpenCart based store than Better Together. An example of this would be "buy two, get one free."