i love my O3.
out of the box, they're ready to shoot. comes complete with bottomline and everything. i love how compact and light it is. everyone who's shot it is impressed...especially when they find out how much it costs. everyone, and i mean everyone...no matter what they shoot (timmies, angels, dm4's, e-cockers, etc), have only had good things to say about it.
the mechanisms of the O3 isn't as complicated as the other markers, but that works to the O3's advantage and it does its job damn well. absolutely no complaints here...well almost none.
eyes aren't really a problem unless you use dark-shelled paint. and unless you take the plastic over off that shields the eyes, it can have trouble reading other paint as well.
this marker needs a delrin bolt. stock bolt works decent, but delrin will definitely be an improvement.
that's pretty much it... and if you want to increase performance still, you can slap on a QEV. click here
for an example.
as for the barrel, it shoots pretty good for a stock barrel. i'm using an ultralite right now and feel between that and the stock barrel, i won't need a barrel kit.
i don't think there are any videos of ppl shooting it in semi mode but there's on going full auto on the odyssey site.