I was no where near the acclaimed max. loading capacity; under 12lbs for sure. Most of the time, not even that heavy, more like in the 5-8lbs range. My heaviest setup was Nikon D300 _ Sigma 50-500mm lens or Sigma 28-70mm f2.8 lens. No matter how hard I was trying to tighten the knob, the head was still shifting under the load. The drag/friction knob didn't seems having any effect on this. Eventually, I replaced it with an Arca Swiss B1 and behold, the problem was gone.
I have to say I was fascinated by the look and design and that certainly had a role in driving me toward this head, being so unique. But I didn't think it it might fail like that in practice.
This was a couple of years ago and since then, I have been using my B1 which I just recently sold since it no longer serves my new needs. Hence I am again looking into the market. I have realized some innovative options are now available in the market. This includes some newer Acratech products. I am not excluding them from my consideration. I like that they are light, compact and have multi-purpose functionalities and that they look good. The GP for example has the goods of both worlds: it is a ballhead but can provide isolated tilt (and pan) motion(s). Even better is their video ballhead if it wasn't so pricey.