The synchronous design uses two sets of opposed magnets to achieve the desired torque. The result is a noisy, ratcheting effect.
In the hysteresis design, the magnets drive the torque through a special material called the hysteresis disc. The hysteresis disc generates a completely smooth, highly repeatable torque to the bottle cap. The result is better torque to the cap and longer life for the clutch.
Contact CGB for more information.