Hi Reportage
Some of the pricier ballheads have higher load to weight ratio, and can be pretty lightweight.
The better ones are more rock solid and do not creep loose easily once you tightened the knob, and are blessed with very smooth ball movement ( which you will have to compare with the higher end ballheads like the Arca Swiss for example to "feel" the difference ).
While creeping can be a nasty problem in composition and stability, I would not loose too much sleep over a ball having less than a pleasurable silky ball movement ( but once you used one you might just be addicted ) .
Ryan