Just so you know, I vote Emperor, lol. I have 2 400's and 1 280, and love them. I'm not an AC fan myself, never really liked them. As for flow control, both the 280 and the 400 have flow control for reducing flow, and you don't need powerheads with the 400. But it's like with any HOB on a longer tank like a 55G, if the HOB is on one end, the other end of the tank won't have much current and may need a powerhead for some flow. I have 2 400's on my 55G because I got them on a cheap sale at Big Al's about a year ago, were like 38.00 each. So no need for powerheads as I have an HOB on each end of the tank.