I have the no. 15 crease brush, its very nice and made of hair. the quality's as good as mac. If the half-moon brush is like their fan brush 22, you can use to apply all-over powder on your face, particularly if you're going for a glowy look, so as not to pile on powder. Also, the fan brush is great for applying very pigmented blushes.
check out their application videos, which is under the tab "Insider secrets", which are really good.