Sorry Rich, missed your question.
Microballoons are generally available in glass (white) and phenolic (dark red). They are the basic ingredient in almost all lightweight fillers.
The West line of fillers incorporate additional ingredients, most of which are equally common (for example, talc, styrene, and wood fiber). Obviously different blends impart different properties. In my opinion, those property changes are of little value to homebuilders. For sure the West blends are very expensive compared to stocking the shop with ordinary glass micro, flox, and cabosil.