when i was looking at them, the MA used medium dark on me as a bronzer. i don't like the look of bronzer, but it looked nice. i bought medium to use as a light powder foundation. but they certainly work if you like bronzer!
I tried dark (I'm lighter than an nc15) to use as a bronzer. It doesn't look garish though, indeed it looks mighty fine and gives me a sun kissed glow. It's far superior to most bronzers, because it ISN'T glittery. I like it a lot.