I've tried them side by side - one box with straight Cat Attract and the second box with Elsey's Precious Cat with the powder sprinkled in. The Cat Attract box got a lot more use than the one with the powder.
I have to agree with Amy - let your cats tell you! Some of mine prefer the litter, some prefer the additive (partly because 2 of them only use a certain texture of litter - and cat attract litter isn't that texture