The tension rods with bearings stop 100% of the front to rear movement that you do not want. The bearing unit allows the suspension to travel through it's range without any extra pressure. A bushing in that area, fights the suspension, and does not allow it to travel as easy. The original ES bushings were so firm, that not only did they limit travel, they broke the lower control arms they were mounted to. The ride quality and handling is by far better with a bearing unit rather than a bushing. If the bushing is made softer, it allows the wheel to move forward and back as well, this is not desirable.