The only Australian thing about Uggs is the name which was used in Oz to describe sheepskin surfer boots.
Uggs (TM) are owned by Decker and are an American brand. Yes, they took an Australian name. There are more than a few copycat Australian brands selling sheepskin boots that claim to be the 'real originals' or somesuch. Most look shite tbf. There is a British company, Celtic, claiming the same thing (or it was last time I looked). Their boots are not bad at all but are almost the same sort of price as real Uggs, and do not quite have the Ugg styling.
I have several pairs of Uggs. I even have a very old pair that were actually manufactured in Australia (no idea why Decker had them made there), but all the rest are made in China. Most have a proper grippy, cleated sole. About half are sheepskin-lined leather or nubuck - ankle and biker boots. Most are completely waterproof - I usually choose those.
The other real plus point of Uggs over other brands is that they are not fat and clumpy looking. They have a good boot shape. I don't like the look of Emus for example, they are just too big and puffy on the foot. Bearpaws are a good shape but are made of cow suede and usually lined with nylon fur = smelly feet.
Most of the TKMaxx copies are not real shearling inside. Some are just on the top part, but not inside. And they are too expensive for a boot that will only last a few months - Primark would be a better option.
Some are good though - check carefully. The heel needs to be hard and rigid to stop the foot sliding around inside as this stretches the delicate sheepskin = that appalling walking on the side of the boot thing that you get with fake Uggs.
I buy Uggs mostly in the sales at Ugg uk and at Office or John Lewis. The reason that they are worth the price is that they keep their shape, they keep their looks, they last forever, and they are extremely comfortable. I put them on the Autumn, and take them off in the Spring.