The main difference I see with the emperor, is the spray bar that keeps the bio-wheel turning even if the cartridge gets totally clogged. This is good insurance, between the emperor and the penguin, I would always take the emperor. The spray bar does have some drawbacks, if you adjust it wrong it will water your lid like a lawn sprinkler. The HOT magnums are quieter with less evaporation, so might be preferred in a show tank, but since you have to remove the whole filter to clean, should be used with a second filter.
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