Yeah. I think these makers don't know anything about what they're talking about - at all. The designer is a copy-cat goof-ball who probably never held a camera in his life. I mean WTF, magnetic direction compasses stuck sideways in two knobs? And for $100 delivered... I'm certain there's no QC, and no testing done on these. So that 8kg or any other specs they mention are just picked out of thin air guesses. It might be 8kg, it might be 14kg... 8kg seems a little light for this particular unit tho. I bet I could lift up the front end of a '72 VW bug with this thing - no problems.
I just tried hanging a 15kg barbell weight off the arca-swiss release knob while my camera and a Sigma 500/4.5 APO lens was mounted and it didn't seem to phase it. Totally I guess that's about 18 or 19 kg and it had the same smoothness in all directions - as could be tested. I guess I would totally trust this thing under all circumstances with 15kg mounted. But that's just another guess tho. Like Lars pointed out; if you're long lenses are high-dollar units then you probably have the money to get the real deal and that's going to feel better all around anyway (emotionally, ethically, sense of secureness, etc.).