There are two separate arguments going on here...
1)Is the knock off a viable part from a suitability point of view
2)Is the knock off a viable part from an ethical point of view
To address point 1, ARBs test shows that system failure for the knock off was within 7% of that of the original part. assuming manufacturing tolerances etc etc etc this seems like an acceptable variance. Whether your axle or your diff fails makes little difference trailside if you do not have the correct tools, parts or know how to do a jua kali fix. It could also be argued that the knock off may have inferior wear and tear, longevity or usability. All these points may be true, however there is only one piece of empirical evidence in these areas, that is that ARB chose not to address them, which would appear to indicate that the greatest area of weakness of the knock off vice their product was strength of the components.
As to the ethics of the issue. The engineering of the part has clearly been stolen. This must however be weighed against ARBs pricing structure. Assuming that the engineering work has been done for a given design, and that those costs have been defrayed, marginal cost for producing an additional cost would come down to variable costs for that particular unit (material, supplies, manpower et al)... these are relatively tiny. The only other costs involved are advertising customer support and the like. As with any industry, brand recognition pays a large part in product selection, and allows a company to charge massive premiums. It is my contention that this may be why ARB's price structure is so high; it is not that they have a vastly superior product, but that they have the perception of a superior product. Unfortunately perception only goes so far, and attempting to maintain a premium price structure in the face of cheaper, functionally equal rivalry is futile and best and usury at worst. It comes down to the individual consumer to decide which is worse... to let a rival steal intellectual property or to allow a company to charge monopoly prices...
As to the argument of not buying Chinese; most I have talked to appear to be missing the point. In order to strengthen the domestic economy the answer is "Buy Local" not "Do Not Buy Chinese"... sending money to Australia does as much damage to the US economy as sending it to China. In this case it actually does more, as on a per item basis one must spend several times as much money. To put it another way, the problem is not that money is going into a foreign economy, but that it is coming out of a local one... Sending $100 to china has about a $150 long term effect on the US economy, sending $100 to Australia does exactly the same thing. What we are talking about here though is sending 400 to china vs 1100 to Australia, and the second is far more damaging.