people on wowhead are saying otherwise about overwriting the buff.
he does say, however, that it was pretty much always up so my argument is void and null.Not only is the proc rate extremely high, but there is also no ICD and it can refresh itself. In about 15 minutes of testing I got the buff on every opening Mangle, and it always refreshed on subsequent Mangles - the buff does not have to drop off to get reapplied.
Basically this is a +153 AGI idol for any bear tank who uses Mangle at least once every 12 seconds... i.e. all bear tanks!
A massive upgrade from our level 70 idol. /mourn the passing of Idol of Terror