I had purchased the slow meter (6) ball at 925 cr, then I changed over to slow meter (6) ball for 600 cr, It is apparent that the lesser cost ball does not keep the same ball speed as the more expensive one, meaning cheap ball is much faster on the meter bar.
So my thought is they want you to buy the more expensive balls. I have seen a increase of poor game play from my previous games not being able to control the stop point.