No experience here but an SSHD, like a restaurant set menu, a package holiday or an integrated camera, is parts bundled to offer the consumer value for money. Easily satisfied consumers like bundles. Picky consumers dislike the compromises and prefer to combine their own choices. You are assembling you own computer so the separate component option seems to better match your style.

Usage patterns are individual, flash endurance numbers are hard to verify. Several of my SSDs outlived their host laptops. Their work was mainly compiling and unit testing, the heaviest load was sometimes running virtual machines. My Raspberry Pis use their original SD cards from several years ago without errors whilst other people have seen short card lifetimes, so my demands may be too light to be relevant.

Your worry might be what happens when the flash wears out. Hopefully the decent ones degrade gracefully, gradually giving less performance benefit and sending warnings to monitoring software. Personally I am cautious and would recommend the separate SSD and HDD option.