I've knit three of these Urchin hats so far. The first two were from Twirl (cream and cranberry) in sizes medium and small. The medium turned out enormous (platter-sized) but was liked by its recipient regardless. The small turned out very nicely, if slightly fuller than pictured in the pattern. It takes a little more than one skein of Twirl for the small hat, and the spiral pattern doesn't really come through with the boucle yarn, but it's very cute.
I also bought two skeins of the Cadena in Neptune to make the plain-yarn variant for myself, but I'm very underwhelmed by how it turned out. It used less than a whole skein for the medium size, but I'm not sure that a large size would be better. Maybe this yarn is just mediocre.