'Whitest ever' paint reflects 98% of sunlight

conventional wisdom says -never use pure white or pure black in a painting. So the whitest white would not be of much use.
Using the 98white as a ground might be useful. If you were to paint transparently over it, I would think the colors would be more intense than painting over a white that was less reflective.

As a mix, it might have the opposite effect. When you mix white with a color it becomes lighter, cooler, and less saturated. So if you mixed a whiter white I would expect it do and even better job of making the color lighter, cooler, less saturated.

To reflect 98% of the light that hits it, it must be very opaque - otherwise it would lose a larger percentage of light to transmission.
So if you mix it with a color - say red - when light hits a red particle in the mix it will reflect red, but when it hits a 98white particle it will not only reflect red, but also green - it's compliment (and every other color). So there would be no savings in chroma.

When it's used as a ground things are different. If you applied transparent red over the 98%white - the 98white will reflect the color red and only red, since that is the only color hitting the 98white as the red coating would prevent any other color from hitting it.
Nothing new about using Barium Sulfate in Artists oils. MFGs have been doing it for years. The older Grumbacher tubes have it noted as an ingredient.

I guess what’s different is the various particle sizes they are using in this new mix to make it more reflective.
Ha ha! It's bad enough hearing the controversy over, zinc, lead, titanium, flake and every white ever created, now there's even another to add to the mix... :)