Puppy. The problem with really thick chain is weight. Undo weight in your chains is the fastest way to shorten the life of your grips. Also, bike cable isn't nearly as flexible as other chains making certain moves impossible. and finally, the rotational stress imposed by spinning requires that the cable be attached to a spinner to prevent it from twisting, warping and breaking. Such spinners are notorious for sticking causing the same stress as if they weren't there.
Ball chain is all spinners so there's never a problem there, and it almost never kinks making it the best choice for poi. This is a delicate art of direction, not control. any change in the behaviour of the poi in any position can lead to mistakes.
SWL: Odd, I've checked my SS chain at very high stress and have had no problem. To prove my point once, I pulled my truck through sand with my poi. I can generally subject my #10 SS ball to more than 200 lbs. But I'll check into it.