See first rule I learned was don't expect healers to be perfect, thats what ironshields, nightmare seeds, and avoidance trinket cooldowns are for, because sometimes even the best healers don't hit it 100% right, and the 1% they might not is the 1% ardent defender might save you. A good healer won't berate you for blowing an item to save yourself, even if it turns out to be unneeded, its not a lack of trust but a trust with the raid, you do everything you can to stay alive, they do everything they can to keep you alive.
Maybe its the wrong way to look at it, and if I hit T6 content properly I might have to reconsider my views, but in T4-5 that buffer ardent defender gave me even if it was on the occasional Maggie cleaved, hit me, the roof fell in and the healers were on the group for some reason moment leaving me on 12 health, LoH, or Nightmare + Pot put me safe enough for the healers to handle it again. At the moment I don't see trading it as a worthwhile thing since it does proc a lot (seen it 8 times in 1 wave in hyjal, when all that was keeping me standing were flash of lights from 3 paladins - to explain we normally don't bother with cc, other tanks grab banshees, or that, then we just consecrate and aoe everything to death in the entrance way, seems to work well tbh but a few scary moments when the healers realise I just moved oor). Basically if I go down on waves like that its a wipe, so better to waste 5 talent points for the chance of survival imo.
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Ahh, but you have heard of me.
http://eu.wowarmory.com/character-sheet.xml?r=Lightbringer&n=elyria