I've never been in a quad, but I think it makes sense that if everyone is on the same page It would be very stable -- unlike in a three-person situation, no one ever has to be the odd one out when folks are coupling up.
Very glad to hear things are going so well for you all!
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.