Not sure if you know about bioavailability for omega 3 from flax. There are several forms of Omega 3s. Plant based forms are ALA (alpha linolenic acid). ALA needs to be broken down into EPA and DHA to be bioavailable. This conversion is not very efficient compared to taking/eating Omega 3 already in EPA and DHA form. Also, presence of LA (Omega 6) further impairs conversion of ALA.
Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)? - PubMed - NCBI
DHA/EPA Omega-3 Institute - Conversion Efficiency of ALA to DHA in Humans
There appears to still be debate over benefits or how much DHA and EPA are desirable. They each have different benefits physiologically. Both EPA and DHA are plentiful in fish oils and directly bioavailable. Algae sources contain DHA.
My personal take on it is that eating some flax here and there is not a big deal, but excess is questionable. I also take some fish oil daily.