Every little bit helps, plus it will give you what, another 100 attack power from bladed armor and it reduces movement slowing effects on you which is better for PvP but in PvE it can help as well. I haven't checked the exact mitigation it gives me but it should be around 3000+ armor for me from that single talent. Personally I'd rather have more defensive talents on my DK and let my shamans worry about doing DPS.