I just picked up a marineland 24-36" light. I don't like it on my 24x12x10 tank though. My tank is too short, the light doesnt cover the whole footprint.
I put it on my 20g long (30x12x?) and it works well because half the tank is covered by a foam background.
I also tried it on my 90g (48x18x27) and the tank is too high, the fixture isn't bright enough to cover the bottom.
In my short time with it I think the best depth for the tank is about 24". This lets the light cover the footprint of the tank. I also don't think that it will grow plants well because it is nowhere near the brightness of a T5HO. You have to have a tank that suits the light or try it out before you get it if you can. Some will like it and some won't.
I'll be using this on my 20g long though because it lights it up pretty well.
Overall, I'm pretty happy with the fixture because its energy efficient and that it makes a shimmer effect. I'll get another one if I have a tank that suits it.