i liked big ball. i used the yoga ball to stretch my back and chest and as a chair. i push the ball against the wall and work on dantien moment. the big ball gives good feedback. you can also do it using various body parts such as chest, shoulders, back, hips and so on, to remove the dependency on the arms. if you compress the big ball into the wall, it acts as though someone is pushing you in multiple directions at the same time. it simulates someone who has good ground path and soft. i like my ball.
I'm sure that everybody likes Phi's balls...
Here an interesting clip of a Wu style guy (who was actually a prominent figure in pre-war Chinese politics) - check out the golden ball (and the hacky sack!):
Thanks for the kind thoughts David!