100% what ^ they said!
EOC is popular due to its great marketing, IMO. When it comes down to it it is nothing more than a mix of soybean oil and fish oil, with soybean making up a large majority of that mix. All the “transformations” they post of horses gaining weight or becoming very shiny are simply because the owner is feeding oil (ANY oil will do this). The recommended feeding rate for EOC is 4 ounces a day, IIRC. That’s 1/2 cup oil a day. I’m willing to bet the farm that you would see the exact same results from feeding 1/2 cup/ day of canola oil. At $2+/ day it is not worth it at all (compared to canola’s $0.15/ day at the same feeding rate).
If the rest of your diet is in order (as JB mentioned) and you are looking for an omega supplement, I cannot recommend KPP’s Contribute enough. It is fish oil with Total omega-3 fatty acids: 10,780 mg per oz, Eicosapentaenoic (EPA): 3,210 mg per oz, Docosahexaenoic (DHA): 2,320 mg per oz which gets you a lot closer to the amounts Absolut Equestrian mentioned. The recommended feeding rate is 1-2 ounces per day (half of EOC’s feeding rate). It smells amazing - a mixture of cherry and bubblegum - and I have not had an issue getting horses to eat it. It is cost effective at $0.45/ ounce (so between $0.45 - $0.90/day depending on if you feed one or two ounces). I noticed that when my horse is on it she has less inflammation in her body, however I don’t think any one supplement is a cure all like EOC claims.
You could certainly just feed flax for omegas, however, if you are looking for DHA and EPA (only found in marine sources I believe) Contribute is by FAR the best bang for your buck.