Road and mountain bikes have always had different standards on some things. In particular, MTB cranks had needed to be wider than road cranks for design reasons. That’s the explanation for the 73mm shell. You are looking for an MTB BB. You can’t use a 68mm BB.
The item you discussed is most likely the retainer for the ball bearings. They do hold the balls apart. Most BBs aren’t designed for you to service the individual components. Now, cup and cone bearings are designed to be regreased periodically, and you might be able to get individual components possibly including the bearing retainer. That is, if someone sells them - the parts for low end cup and cone hubs or BBs may not be readily available because you might as well replace the whole BB, or hub, or perhaps the wheel (you can probably just buy the individual balls from anywhere if they need replacing). After labor, you would probably be at the price of a new BB, so this may not be economical even if someone sold the retainer.
In general, it’s safe to assume that most Shimano stuff is adequate or more than adequate quality. Now, plenty of us have biases towards items made in OECD countries - that means rich countries, and it would include the West plus Japan and South Korea. That said, I’m typing this on an iPad that’s designed by a US company, but a lot of the parts are manufactured in China. Plenty of bikes are made in Taiwan, or China, or by Taiwanese firms that outsource some manufacturing to China. Taiwan was once seen as cheap. It probably still is seen as cheap, and you can get cheap bike parts from Taiwanese companies. For example, many OEM hubs are made by a firm called Novatec. I think I have heard complaints about their quality (on some models), but I have also heard them praised for being good value for money. Actually, way back when, Japan was a low cost country. My old primary care doctor used to make jokes about low-quality Japanese generic drugs (he used more colorful language). And Shimano makes Dura Ace in Japan, but I think Ultegra and 105 are made in Malaysia. Today, Ultegra and 105 are basically as high quality as DA but heavier.
That long digression was to say that country of manufacture might be weakly informative about actual quality. There can be a placebo effect for buying items made in OECD countries, and that’s fine, but if you were looking to do this on the cheap then that probably shouldn’t matter. You should investigate if Tange itself is a reliable brand, which I don’t have any information about.
