I got one and it's got some pretty good action. As stated, the size is it's only downfall. I have the center unit but mounted it on the end of the tank. It has a nice back and forth motion. It's not strong enough for stand-alone in my 135g but with a couple of PH (Koralias) soon, it will be great! You can also get two of the corner units and do the same without the intrusion of the larger ctr unit. All in all, though, I'm happy with it.

HTH
Steve