This combined targeted resistance means you'll be matching the actual strength curve of the barbell curl MUCH closer (using more resistance when the biceps are in a stronger position). (hardgainermusclebuilding.com)
I personally like Exerbotics since it adjusts to the person's own strength curve. (marksdailyapple.com)
In the deepest position, the resistance is highest and once the athlete is ascending and due to the ascending strength curve, the resistance decreases. (christianbosse.com)