OK, I've never used it and don't know anyone who has but when the stuff came out I was curious, but the guys who abuse it looked stupid and that was my deciding factor. Here's a quote from their site. SEOs help a muscle to break past a plateau (sticking point) by helping the fascia of a muscle stretch.
The fascia is the sheath of tissue that envelops a muscle. It is also the primary restrictive factor in muscle growth.
The more flexible the fascia is, the quicker the muscle size will increase. If you see top professional bodybuilders that have muscle gropus that pop, they have very flexible muscular fascias.
That was from the Syntherol website.