I try to use only ace mods if at all possible because I hate updating them otherwise.
In raids threat meters are nearly useless for healers and I never even have omen displayed. I have it just because the more people that have it the more accurate it is.
Its more effective in 5 mans, but I find it doesn't really matter if I know I'm going to pull aggro or not. I don't have a lot of choice but to continue healing the tank. If he dies I'm next anyway. I just fade as soon as I get aggro and if that doesn't save my ass I run to the tank where it either gets taunted or I die.
EXTREME Q VAPORIZER