I use the penguin 400 (i think) with the double bio wheel. It's a redundant filter for me, but it adds flow and does a good job filtering. It worked great for about a year, then I started having problems with the bio-wheels not turning. Calcerous algae and little tube/fan worms gunking things up. I also have prblems with coralline algae growing on the intake screen. The basin that the cartridges go into is nice because it acts as a mini-refuge, and copepods love the filters inside, feeding off of the trapped detritus. You just need to constantly rinse it out so that detritus build up doesn't add to your nitrate load. The containers or inserts that come with it are great for adding carbon and phosphate removers as well, if you desire it.
