The light-movers have been around for a while, but there's definitely a trade-off. Dana Riddle and others have shown that light absorption is cumulative, so that you'd have to make up for less light with a longer photoperiod.
So, picking some numbers out of the air, let's say a coral would thrive under a 250w for 8hrs/day. Put that same coral under a light mover with the same light, and you'll get less growth, since it's only getting part of 250w for the same 8 hours.
Of course, there are a number of factors involved. Many corals reach photoinhibition at a certain point, so no additional light will be beneficial. And, as William said, you wouldn't want it on a display tank...
