This is the beauty of internet hype... people are dropping alot of money on pivots with minimal understanding of how they work. (and i mean that with no disrespect)
The px series were stationary heels, but the old p 12's pivoted. That part of your post is confusing..
The pivot technology used in your bindings has been around for decades actually. The heel piece has gone virtually unchanged. The only major changes in this binding have been the toe pieces over the years. They should spin 360 unless anythings changed on the new ones. (I've heard rumors there were minor changes to how the brakes work)
I haven't looked at the new ones so forgive me if I am wrong about colors. There should be a white tab on the back of the heel. There should also be a small black line near the back of that tab. The two bars on either side of the heel spring should have Philips screw heads on them and adjust your forward pressure. You adjust the forward pressure until the tab is appropriately lined up with that mark. Your din will only change the spring tension in the heel piece. You should have this done properly by a shop tech, but its always good to know. The forward tesion on pivots has a tendency to loosen after alot of riding.
And your final question was why pivots are good? In general, springs that are in the heel piece (instead of horizontal along the ski) have better elastic retention. But furthermore, the pivot technology changes where on your boot the binding will release from. On most bindings the boot will release from twisting at the toe or twisting at the heel. The pivot moves the release to a twisting motion from the middle of your foot. The twisting motion from the middle of your foot will feel alot smoother when you fall, is more natural, and is less stressful on your knees.
