I use this solely as an under eye brightener, but in a pinch it can be used as a concealer. I use this under my eyes in long strokes going outward, like rays of the sun. Then I blend. This looks much better than just applying a little bit just to the circles under your eyes. The product gives a nice healthy glow. The color is very, very fair (which is why I wouldn't choose to use it as a normal concealer), but adds to the brightening effect.
The only annoying thing about this product is that you can twist the end until it clicks, and it seems like nothing is coming out. Then you twist it again and it's a flood of liquid! However, the product works so well that I don't mind it.