So there are actually 3 arms in the design and it is hard to describe what I mean. I personally think that GS has a bad design here. The pegs look like they are very adjustable, but in reality, there is only a couple of positions where they work. So one "arm" connects between the bike and the peg (actually it connects between the bike and a connector to the peg itself). This is the arm they show rotating around in the animations on the GS website. However, because of the way that it connects to the peg, it can only sit at certain angles. When the arm is in "up" position (say 12 o'clock or so), the peg sits above the height of the passenger footrest. So when my wife puts her feet up there, they stretch her hips in an uncomfortable position and her knee is actually more bent than on the footrests. If the arm were shorter, her feet would be below the height of the passenger footrest and she would actually get some extension on her knees and more relief on her hips.
That is why I say the design is bad. Both for the length of the arm and in the limitations on what angles the arm can effectively connect to the peg.