There are always differences. There are always reasons why something is cheaper. Some of these will not be apparent by just looking at the stuff. And it is not always easy to research the reasons for the variation in price. Always assume lower quality whe the price is low. Never assume the products are the same.
Production methods and cost of labor are factors.
Materials vary and aluminum thickness is just one factor. There are also the core composition, the adhesive and the paint. These are all variables that can be manipulated to achieve a lower price point.
Often these things do not matter for sign work. Sometimes they do. Experience may be the only real way to know. It's "buyer beware" to a great extent.
A word about "Chinese versus non-Chinese" manufacturing. Don't be too quick to jump on the "Chinese is always junk" bandwagon. Where do you think your smart phones are made? Chinese manufacturing and technology are cutting-edge. They can do anything we can do. Anything. It is said that Chinese nuclear reactor technology is ten years ahead of the US. And that's just one example.
But....if we want it cheap, they can make it cheap. They make whatever we want. Pressure from US buyers and distributors will always be accommodated. And they can supply things quicker than our factories can. They are more nimble. (cheap labor? Sure. Whatever. It doesn't matter. It is what it is for whatever reason).
Steve Jobs reportedly told President Obama that US manufacturing could not meet his needs, but the Chinese could.
In the paint world, price is usually an indicator of quality. Is it the same in the ACM world? Who knows for sure? Track what you use and how it performs. That's all I know to do. Asking the question on this forum is good. Poor quality goods usually are exposed with time.
Brad in Kansas City