See Labdoor.com and Consumerlab.com to verify supplement quality.
There are some good meta studies on Omega-3s. Dr Bradley Stanfield[1] walks through Mayo Clinic meta analysis[2]. Rhonda Patrick[3] is the best resource for an interpretation of the data.
TLDR; consume enough omega-3s (DHA/EPA) to get omega-3 index above 8.0. Discrepancies in research outcomes are attributed to study design, methodology of measuring intake, methodology of measuring blood.