The assymetric fins have now been replaced by fins that are just a short and fat but do not have the assymetric shape. They work by being very upright, like a slalom fin giving lots of lift but unlike a slalom fin they are very short this means less lift so the effect is as much lift and drive as a swept fin without needing to be as long. Generally a 22cm freestyle fin will give about as much lift as a 25cm wave/freeride fin. The bonus is that the short fin does not need much pop to be out the water when spinning round the moves. The drawback is more spin out and slightly reduced carving performance.
I think the assymetric fins worked because they were also upright, but their outline shape had no bonus and gave really poor carving performance.
Hope this is helpful, also an extra tip for advanced freestlye is to had your fin right at the front of the box (unfortunately not an option for power box), and more importantly learn/practice you moves on a TurfDog Dirt Windsurf Board!!