The preparation of Omnadren is quite similar to Sustanon, and is different only in that 100 mg/mL of it (of 250 mg/mL total) is testosterone hexanoate instead of the testosterone decanoate used in Sustanon. For this reason, Omnadren has a shorter half life, and will give a faster initial increase in blood level. This accounts for the claim of increased water retention and increased side effects, since levels, at first, are higher for the same dosage. Omnadren is cheaper, but Sustanon is much better in my opinion.
There are a shitload of fake Omas floating around the east coast. I wouldn't trust buying any, except for maybe a dude that goes to the country that makes them and picks them up from the pharmacy.