I've never used one but I've seen the efect. Mostly, there are some composed of red leds, that give an awesome dim ligth to watch the fish in the dark. I think this is great for a rocky enviroment with fast moving chiclids.
There's also the blue led strips, that will give the look of a full moon light, specially if your tank has tall plants that will cast shadows over the susbtrate, and you have slow moving fishes. Imagine a heavily planted discus tank in a low dimmed blue light. Awesome.
Red looks like a lot of energy, and blue is calming, to my personal choice.
I never considered one of those since I have my tank in a room with a dimmer wall switch, so I can leave a low light to watch the fishes without bothering them, but now I want one.