The flora in your intestines convert the flax oil to EPA/DHA, but they only convert a small portion of the oil.
I've experimented on my self with them all, even though I was naturally prejudice against old fashioned Cod Liver Oil , it turned out I could really feel the difference.
Not to mention it's the cheapest.
Like Epsom Salts , sometimes the old fashioned health cures beat all.
The health professionals will rarely admit it because it cuts into their bottom line.