Nivek is right on: the (carbon) highback is not too rigid torsionally, that's why you could use the MC for park, and it will give in on a hard turn. Don't know about TRice, but JJ was rocking Spark binders a couple of seasons ago (I use them too for bc, and the new Burner straps + buckles by Burton are awesome!)
I wanted the MCs with the Vans Cirro boots - there are 2 removable stiffeners in each tongue, so I can choose how stiff I want them and even carry the pieces in my backpack to change mid-day, and that's without playing with the boa to tighten them more or less, very versatile. With MC On my Smokin Superpark + Vans Cirro, I can hit park, double diamonds + slack-country in the same day, on the same setup. Sure, I'd take my NS split + Spark Burners + Deeluxe Spark for a real backcountry day, and maybe even for a dedicated lift-served slack. But for anything else, I feel I can use just one setup. My only problem is that the Vans liner is not as good at locking my heel as either Deeluxe or Burton, I may need to switch or even buy a new Intuition liner next season
I would not be opposed to riding Burton Diode or similar as high end Burton binders are very solid. But Union is local and always treated me well, and this is important to me.