How do they use it and still get good seperation?
Their lean as hell. They're probably going to get good seperation based solely off that fact alone. You'd be better off asking someone at the top level that uses the stuff though I'm going solely off conjecture, but most of the idiots we see admitting to SEO use on the Internet are fat balls of sh!t. Most don't even lift. Body builders pumping a little synthol into a muscle precomp will look a bit better.
Think about it this way. The only muscle you don't hit in the pump room pre competition is legs. Everything else looks more full and separated from the mass quantities of blood drawn into the muscle. Why wouldn't results be the same using SEO?
Also, sight oils are a little more permanent then you think. Why are Valentino's arms still the same size? Not like he kept them inflated in prison. SEO stretches the fascia the same way fst7 does. It allows for more growth.
I've never used a sight enhancing oil and probably never will. However I have done a bit of reading on the subject, hop over to pro muscles forums and put it in their search bar look it up. Tons of great info about why who how when and any other question you or anyone else can ask about synthol and just about everything else.