The biggest advantage is that whilst the wiring grommet joints had a millimetre or two of wiggle room the bearing joints have practically zero play in them. This makes the movement of the robot a lot sharper.
The older arms with the rubber grommets limited the range of motion in the roll, sway axes.
SR2 comes with 2 main arms, a pitch link and the 4 bearing end rods.
SR6 comes 4 main links, 2 pitch links and 6 bearing end rods.