"Update: After poking at this more, it’s possible that Apple is using a simplified tier structure in which entire files are moved to the SSD and backed up the HDD, rather than a more sophisticated caching mechanism."

Sensational blog post. Extremetech couldn't be troubled to follow through with due diligence, it apparently doesn't have any journalistic integrity, or editorial review. They literally falsely accuse a company (right in the blog title) of releasing an overpriced commonly available product. Then, at the end of the article excuse their horrible research, by starting with the sentance "it’s possible that Apple". Shouldn't Extremetech know what Apple is doing since you just finished writing a scathing blog post about it??

In fact, they are not caching at all. Extremetech completely blew it on this article, either revealing their lack of professionalism, bias, and/or, both.