In the One:1's anti-roll bar (ARB), instead of using a long bar in torsion to transfer energy, they use the central beam (in the MOC, it's a #2 connector) in bending to transfer the energy during roll. Essentially, the Z version has flex, just in that central member.
Also not quite While you're kind-of right about the 'give' of the roll bar, it's less about bumps and more about cornering. Essentially, the more a car rolls or leans in a corner, the less grip you have on the inside tires, which decreases your maximum cornering speed and the stability of the car. The anti-roll bar transfers part of the load from the outside tire to the inside (minimizing the roll), while having enough 'give' (storing energy via twisting (or in this case, bending the central link of the z-bar)) to allow the car to go over rough patches in the road and also roll a slight amount (some roll is good for mechanical grip).
Hope this clarifies it a bit