My only concern with buying batteries from an unknown source is that defective Lithium Ion batteries have been known to explode. Lithium Polymer is even more volatile. While must of the circuitry to make it safe (i.e. by regulating voltages) should be in the computer, the fact that they've recalled batteries before (though a large part as a precaution and due to public pressure) suggests that faults can be in the battery. That said if you crack open the plastic, you might be able to see if the actual cells are from a quality source. Buying from a local source at least means they've hopefully taken the effort to ensure the product satisfies local regulations.

The the price Apple is demanding here is certainly extortion and makes buying after market batteries particularly tempting. For some reason the people managing Apple Australia charge especially high prices here, even when our currency isn't doing all that well. I guess its a way for them to claim higher salaries.