Ok you are losing a crap load of strength and agi crit aggro, though you gained 10 block value, which helps for aggro on shield slam unless you are already capped for it.  THough as you will see, prot paladins have the same kind of loss for aggro taking this faceplate but more mitigation as you see compared to your warrior tier 6 helm.

Here is the breakdown for tier 6 paladin tanking helm:

Faceplate vs. Prot paladin Tier 6 tank helm

1532 armor - 1483 armor (+49 armor)
0str - 0str (str is useless for tankadins, just want block value instead. str only helps warrior aggro, we take spell dmg instead)
4agi from red gem - 0agi ( 4 agi.  The dodge and armor is useful for prot pally)
82!sta - 67sta (+150hp)
Meta and Red Socket - Red socket instead of yellow socket
30defense - 28+4 from gem defense (-2 defense rating)
38! dodge rating - 37(+4 from socket bonus)=41 dodge rating (-3dodge)

29 block rating - 0 block rating (29 block rating increase.  prot paladins don't care bout block rating. we are uncrushable permanently with holy shield up with kara gear or higher. 8 charges in 8s.)
45 block value - 0 block value (+45block value)

So for a paladin tank in terms of mitigation, one would gain 150 hp (170 with talents), 29 block rating which is kinda useless since we are way above uncrushable at hyjal level, and 45 block value and 49 armor.  The +4 agi with the -3 dodge loss and -2 defense loss breaks even. In terms of mitigation, this faceplate is better for mitigation.  However, in terms of aggro stats, while warriors are losing 23 strength and 28 agility for aggro, we are losing 43 spell dmg, probably about equal in terms of aggro stats loss.  I would use this tanking a boss, but for aggro intensive fights or aoeing, I'd use Lightbringer helm.

Well Lightbringer is less differential from this faceplate compared the warrior tier 6 helm, which goes to show, Lightbringer tier 6 paladin tank helm is very good, has mad dodge in it,etc.