This in no way should be used as a way to reach the crit cap. That is just a stupid idea IMO since you are leaving yourself open to a bad RNG in something that is so easy to cap.
Honestly, stacking def is your best option for avoidance anyways, so I typically sit at about 570 in my normal tank gear. I did buy this sigil for the reasons listed above. Its an avoidance sigil. Its quite a nice one too for fights like Sarth 3D, OT patch, and more fights in the future. I really hope blizz gives us something similar in Uldar. Its nice having the options between threat (which is my standard sigil) and avoidance.
I cast the spells that make the people fall over.