Difference is the build quality and the features. The MP10 has a controller that allows you to program the powerhead to do wave type activity. The Koralias are just on or off. Also, the Koralia are known to have issues with start/stop (I know this from personal experience, since all my tanks have Koralias in them.) The MP10 also has a "through-glass" configuration where the motor and electrical is actually outside the tank, and the propeller is magnetically connected through the glass. Very innovative design, really.
As far as "cheaper" than the MP10, just about every other manufacturer. The Jebao WP's are fairly new on the scene, controller based like the MP's and shaped and directable like the Tunze's. Getting differing opinions on quality and longevity, but at $69, you can buy a bunch for what one MP will cost you. Tunze has several models at the flow level of the MP10, they also make a controller. However, you'll end up at about the same price as the MP's when you buy the powerhead and the controller.
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