Hardly
Anyone can do what they want but in this case with a illegal cat you might as well just get a decat or straight pipe and still have it be illegal than paying extra money for something that is illegal with less flow. Only problem would be the smell and my old car gave me a bad cough that I still have to this day. Either way, for a V6 running a twin system 2 x 2.5" cats of nearly any brand will flow pretty freely.
In the original post he asks if they are ok for Australian use, I assume he asking that because he wants to know if they legal. That's why I was pointing out the other ones posted are not.
X-plode Performance Pretty sure this guy on these forums does 200 cell metal cats (as well as 100 cell ones) if thats what you are looking for but I wouldn't have any problem fitting the ones that you posted from ebay if they are 200 CPSI.
Ive been going to add a catch can and still might but that wont stop the exhaust gasses going in there and building up carbon. I haven't really read up much on what I need or not for it to run properly as there is ton of hoses and fittings that I'm not exactly sure if its needed.