Sorry, my misunderstanding. The ECB decreed that the Kookaburra be used in the last round and this round of Championship matches, and there seem to be three reasons behind the decision. In part, it's seen as a 'punishment' for Dukes' poor supply of balls last season, when they seemed to go softer and out of shape faster than normal. There is also a belief that players in the County game should have the opportunity to play with the Kookaburra so that it's not such a shock when they are picked to tour with England. Finally, there is the thought that the Kookaburra does not move as much laterally, so this will encourage genuine pace and spin. Take your pick.