Your circular spray brush has a pretty awful distribution of points. If you hold it in one location for several seconds you can tell that it's heavily biasing points to the bottom left, and you tend to get very visible "lines" as well. I tweaked it a bit to improve it:
My implementation still isn't perfect, as it biases points in the middle over points around the edges. (A consequence of the fact that a bunch of points evenly distributed around a small radius are closer together than a bunch of points evenly distributed around a large radius.) But it's definitely better than the one in the article.