No they do not stack with themself. And OG over CoF.
OG will stun minions only, but if you have a primary with an AoE stun suck as Stone Melee this can be a nice combo as OG+Fault will stun lieutenants and bosses as well. Mobs will tend to stagger around a bit which can be a pain with a death shroud or an AoE heavy primary as your mobs wander off. However, it is cheap to run endurance wise, as accurate as your other attacks and has a small health drain that will not be a problem for a brute (health will counteract it nicely).
On a brute CoF will fear both lieutenants and minions. It has very poor accuracy and a pretty high endurance cost (the same as death shroud) it needs heavy investment in boosting accuracy and endurance reduction. It applies a small to hit penalty of 5% unenhanced, which will affect any mob hit whether or not they are terrorized.
Which one you choose is up to you, but for my dual blade/dark armour brute I went with CoF as when fighting bosses I could lock down all non-boss mobs to use as fuel for dark regeneration. In my experience even if run with death shroud, which wakes them from their terror, mobs attack rate tends to fall and being feared they stay put for my AoEs once they are in the CoF. But as mentioned above, it is a bit of an endurance sucker.
@Moondog
Union:
CoH: Moondog (WS); V-Rock (Tnk, semi-retired); Pole-Star (Bla); Demon Dog (Scr).
CoV: Midnight Gunner (Corr); Operative John Doe (Ban); Day-Star (Dom); Commissar Jaeger (MM).
I am a bit confused. So would very much hope someone who has tried CoF and OG to tell me whether the Fear and Stun elements in CoF and OG are stackable by themselves.
So for example: if I switch only CoF on and stand next to a boss, would the fear component of CoF stack on the boss everytime it pulses?
Also, which one worth taking if I am to just pick one?
Thanks