'Tain't so, McGee

Well, now that the Color Parrot has a spiffy new name (two of them, evidently) and a new site and an updated description page, I'm afraid I'm going to have to quarrel with some statements made on that page (I had hoped they would have evaporated in the renovation), to wit:

One of the main problems with most existing white balance diffusers, is that they treat all light entering the lens the same. In other words, light at the edge of the frame is given a similar weight to light at the center of the frame.

I have no idea what that means. Are you referring to light striking the diffuser from different angles (which could also be described, for a limited range of angles, as "from different angles within the camera's field of view", which in a sense could be thought of as "the frame")?

In any case, I am not aware of any diffusers that are equally weighted across any substantial angular range. Several have essentially a "cosine" acceptance response, which is certainly not even approximately uniform.

I won't even bother asking why that is "a problem".

Not only that, by using small pits in the surface, some products specifically attempt to mix all of the different light sources together so the camera will give an average reading for all of the light sources within 180 degrees.

Well, if you are describing the ExpoDisc, the "pits" (a pattern of little prisms) are intended to produce nearly a "cosine" acceptance response (which, as you know, is considered by some to be appropriate for incident light measurement for either exposure or white balance purposes). It does not give "an average of all the light sources over 180 degrees."