I can't speak on the hydor #3, but I do have the #4 and it works great. It has a wide flow and covers a lot of area. I have two that are almost faciing each other at opposite ends of a 4' tank. they are about 5" from the surface and the flow reaches both end, top and bottom of the tank. Also, the magnet connection keeps them in place. I love them. The con is that they are huge. I wish they weren't so intruding.