Just use your own judgement about when to use it. - People saying its useless are probably the same people that value crit over mp5 and still thinks FoL builds are good for raiding.
Its pretty simple; Who would take a filler talent that were a flat 6% incoming dmg reduction? - Thats right, every freakin one would take that. - Now lets add +aggro to that. - The answer should be the same except in those cases you risk pulling aggro because of it.
Are you running around healing inbetween adds that needs to be picked up by someone getting aggro on them? -> dont use it.
Are you healing near a boss that resets aggro? -> dont use it
Most other situations -> definitly use it, 6% dmg reduction is a buff most players would kill for.