Vegan

Yes, I have seen those studies. Some people are better off supplementing, but if OP is not one of those "most humans" with a low conversion ratio, then it's just added worry and monetary expense for little benefit. It ultimately depends on one's health goals; if someone just wants to survive and doesn't care about everything being optimal, then the case for supplementation is weaker unless the ill effects of deficiency become noticeable. If someone does want to achieve totally optimal health, then DHA/EPA supplementation is just the "tip of the iceberg" and one of the most basic considerations. We haven't seen OP's current levels of DHA/EPA, so no one here can really say one way or the other whether supplementation would have any benefit at all at this point.

In any case, if concerns about the effects of not supplementing are a source of stress: take the supplement.

EDIT: Oh, and don't blindly follow health advice from strangers on the internet, especially if they're selling something. Just in case that wasn't obvious.