Though Koralias aren't the only brand that provides this, the thing I like about them is the high flow rate, as well as wide angle (not a super-strong stream coming out as a beam from the powerhead). The K4's only consume ~8-10 W, and provides 1200 gph of flow from a single powerhead. Compare that to the Maxijet 1200, for example, which consumes 20W and only gives off 295 gph. Lower power consumption == less heat added to the tank, and of course the much higher flow rate is great for good circulation.
Other powerheads that are similar to the Koralia (probably better, but similar in the high & wide angle flow rate), are the Tunze and Vortec, but I think they are much more expensive.
The Koralias seem to be a good combo of high flow rate, low consumption, and cheap cost. Keep in mind, the standard Koralias aren't designed to be used with wavemakers. Koralia now offers low-voltage controllable powerheads, almost the same price I think, when can be used with Koralia wavemakers.