AFAIK the new emps don't allow flow rate adjustment, my old ones do, the new ones I bought three months ago removed it. I prefer not having it, as I always managed to close it and starve the filter of water.
Aside from the impeller deal mentioned, the only real plus is the spray bar. Which keeps the biowheel spinning and exposed to untreated water even if the mechanical media gets clogged. In the penguin the water spills back into the tank near the intake tube, leaving the biowheel high and dry, and causing an ammonia spike. Also, the penguins seem to drop in flow rate quicker from clogging and buildup of crud inside the intake tube/impeller area, making it less forgiving if you neglect to scrub it out monthly.