As a general rule, speed/contrast paints work best over highly textured areas like fur and such (because that lets it do its contrast thing and concentrate in the recesses), and less well on large smooth areas. On a typical RPG character miniature, it's pretty rare for there to be smooth areas big enough for it to be an issue, but it's not great for things like vehicles.
I think this mini illustrates the difference pretty well: the fur looks nice, but the torso is a little splotchy.
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