Evil is kind enough to constantly install improvements in the omens as the production goes along. Thus you don't see them releasing a lot of upgrades since the newer ones have all that they currently have.
When purchasing an omen make sure it has the black trigger and larger guard and you'll be fine. That's the most up do date one and is a later production model.
The chip that Chris_PDP makes is an upgrade to the current chip... a cheap but valuable mod. You can also install a morlock if you want more control, but lets not go there.
The stock barrel is supposedly as good as any aftermarket barrel out there. I found it to be pretty good, but I'm all about paint to barrel match, thus the pipe.
Where do you buy it? I suggest Shadrach, simply because he's a reputable trader here and sells for about 380, but I suspect you can get him to compromise a little more...