* Full employee status, including pension benefits. You're still underpaid of course, compared to market rates. This also addresses issues like parental leave and holidays.
* PhD contracts are fixed-term, 1+3 years. If you are given a third fixed-term contract, you are entitled (by law) to convert your contract to indefinite term. This makes it hard to keep around students for longer than needed as cheap workers.
* The typical format for a STEM PhD thesis is "story chapter" + peer-reviewed publications in verbatim. Which means you can spend more time on research instead on an exercise in futility.
* PhD defense is purely ceremonial and timed. OFC, you can still be made look like a fool.