Correct!
When "unless" is attached to a two part idea, we're going to negate it ("If-not it") just like we're doing a contrapositive.
If you were looking at a conditional like
______ ----> B and M
and writing a contrapositive (writing an "if not") you'd have
~B or ~M --->
Unless is doing the same thing. It's negating that whole idea. Unless is saying, "If it's not the case that [i]it was intended to benefit and worth more than customary"