This concept was very popular back in the days when computers used to boot from HDD, but now it doesn't make much sense. I wouldn't notice If my laptop boots for 5 sec instead of 10.

At the time of their introduction Optane drives were noticeably faster to boot your machine than even the fastest available Flash SSD. So in a workstation with multiple hard drives installed anyway, buying one to boot off of made decent sense.

If they had been cheaper, I think they'd have been really, really popular.