I use this (like almost everyone on here) as a contouring powder, and for the price it's hard to beat. First, I'm surprised to read reviews saying it's good for fair but not for tan/darker skin tones? In my opinion I would say the exact opposite. It's the exact colour of a natural shadow, and looks great on my NC40 skin.
The product can be tricky to master. I agree it can be patchy/muddy/too harsh. The trick is to use a CLEAN brush (you don't need to wash the brush each time, just swipe on hand or tissue to get rid of residue on the bristles). Start with a really light hand and little product, because it can look muddy real fast. I apply this before bronzer and blush for a more muted look. Also, I find its really easy to go overboard with this (a little goes a long way ppl), but you can take away the harshness blending it in with bronzer and/or blush.
Bottom line: if you think the colour is right for your skin, I recommend trying it. It's cheap! Can't go wrong with a VERY light sweep and lots of blending, but be prepared to practice and figure out what works for you.