If you read the disclaimer on the bat, it clearly states that, over time, it will lose all the helium. The drop has to be -3 with the helium, so IF the helium is having any effect at all, two things would be in effect here. First, over time the bat will become heavier overall, so it will remain within the BBCOR, -3 spec (may become -2.999). Second, the swingweight (weight of head relative to handle, i.e., weight distribution). IF the helium is having the effect of lightening the bat, mostly at the head since that's where the greater volume of helium is, then the swingweight would be lighter early in the bat life, but get heavier as it loses the helium.
My personal opinion is that it's marketing hype and nothing more, and that the helium is having no performance impact on the bat that would even be measurable. So if you like the bat as twoway's kid does, get it.