They have a broader flow than a traditional power head, but I like the one I have. The fact that it uses magnets to stick to the tank is awesome (hate replacing suction cups!!).
I use two of them on my 165 (6'x2'x2') and the flow of each one reaches about half way in the tank (3'). There is a small piece on the end that creates a wide, gentle flow (easy on plants). I'm not sure how they'd do in a saltwater tank as I don't know how the shaft would hold up.