I am so happy I never learned about 'normal' alternative relationship rituals until long after being involved with multiple relationships. lol
Couple-to-couple always struck me as more work, and more prone to 'jealousy', or insecurities, not less. It doesn`t mean I shy away from it, but when it is couple-to-couple it`s in your face more, you see more,..therefore there is more to deal with.
Individual relationships can be tucked neatly aside, and interactions and knowledge happen on a need-to-know basis.
Entirely my own experience, as someone who is in a open marriage, and has experienced both individual relationships, and couple-to-couple.