> Kaeshibashi

The preference is to use a separate pair of communal chopsticks that is not used directly for eating.

> Kosuribashi

I have heard that this one is because it's considered to be an insult implying that the chopsticks are low-quality. (That said, if your chopsticks are indeed low-quality, then avoiding splinters is probably preferable to then visibly plucking splinters out of your fingers.)

> Just proceed to eat some splinters, then? What is the good etiquette way to handle low quality el-cheapo chopsticks?

Well first of all the chopsticks are joined at the non-eating end, typically. So the splinters would be bothering your fingers more than anything.

It's rude because it insults the host, in a way. Anywhere that would care about you doing it should not be giving you the cheap chopsticks in the first place. If you're in a place that gives you them, they probably don't care about you doing it.

I think it's important to point out that these are good manners for eating with Japanese people, not good manners for eating with chopsticks. There is no requirement to emulate Japanese eating manners if you're not in Japan and not anywhere near a person raised in Japanese cultur. There are other cultures that use chopsticks that do not necessarily have these manners.

The disposable wooden chopsticks in Japan don’t splinter (they’re higher quality and cost more than the ones we have in the US).

That’s why you don’t need to rub to get rid of splinters.