Pedro, quite a bit of what goes on in the way of service part changes on carburetors is driven by reliability difficulties in the US. The underlying problem is keeping flexible parts such as diaphragms alive when they add substantial amounts of oxygenates to most of the fuel. The oxygenated fuel, sometimes described as "reformulated", consists of normal petrol plus ethanol and various ethers such as MTBE. Those additives tend to be slightly aggressive against gaskets, diaphragms and hoses, especially those based on the older elastomers from before about 1986 when the US began encouraging reformulated petrol. My guess is that the mylar diaphragm you are talking about is mainly a defence against those additives. However the additives can be avoided in Australia since oxygenated fuels are not mandatory here, and those that do have ethanol in them are usually labelled at the pump. Hopefully most Outdoorking members are aware of the perils of ethanol and do not buy petrol containing it.
If a reputable repair kit only contains one diaphragm, and it is one of the traditional black ones, I think it is likely to stand up pretty well to Australian fuel that does not have ethanol in it. It is after all, the same as the original equipment diaphragm that came with the carburetor when the machine was new.
