The penguin 330 is the exact same size as a regent 30-60 that you can get at walmart. they are the same thing except the regent has no bio-wheel. I have a emp. 400, 2 emp 280's, and 2 penguin mini's. all great filters with bio-wheels. the main difference between the penguin and the emperor is the emperor has a spray bar to drive the bio-wheel and has cartridges to put whatever media type you want in addition to the standard carbon cartridges. I don't use the carbon ones, just stuff the back of the filter with floss and I fill the changeable ones with floss as well. The penguins are just regents with bio-wheels (nothing wrong with them, great filters) the emperor series are the true performers but do carry a higher price.
hth
Richard