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They're not. They're very similar but there are a few other differences. Mostly the finish and the attached pieces. At the core they're probably the same bit of metal.
Also the price difference is about the cost of a good set of brake pads with replacable shoes so they worths.
I'm not saying they'll work a load better but then Ultegra doesn't exactly work loads better than Tiagra (which is what these two calipers are equivalent too).
Bit late for this, but it's the same brakes, the only difference is the shoes.