I was under the impression that flax just gives you ALA not EPA/DHA, so you won’t get all the benefits of fish/krill oil with flax. The latter two are the ones that give the biggest benefits.

Eg https://www.nordicnaturals.com/healthy-science/is-eating-chi...

Only ~10% of plant based omega 3s is "useful" - https://www.health.harvard.edu/heart-health/why-not-flaxseed...