It's an interesting defensive combo for some Mage characters. With the staff, enemies nearby are automatically Chilled, and if the Chilled status is enough to trigger Ice Armor, you get two 50% bonuses to damage reduction. That should make Melee attacks laughable, since my math is dropping damage taken from any physical attack by 75%. Knight Enchanters don't need it, of course, and it could be argued that if a Rift Mage needs it, you're doing it wrong, but it's an interesting choice for other characters. And it is nice to have a way to Chill enemies for Winter's Ruin without having to use up an ability slot.
That said, I don't think it's worth losing the offensive bonuses provided by either Encore or Wrath of Lovias. It seems to me that 31% Attack boost isn't that great, though I will admit to being unsure what the max Attack value the Encore can get is. Plus, you miss out on the extra buffs that the Encore gives, as well. That's just my opinion, though; with my luck, someone will slap me in the face with math proving that I'm wrong.
No slap, but just eyeballing the stats, 31% attack is nothing to sneeze at IF Ice Armor is always on while wielding the staff. Physical invulnerability, even capped at 80%, makes for happy times. I ran through most of Trespasser with Ice Armor on most of the time through Ice Array, and could give those Qunari spear throwers a wink and a nod -- they couldn't touch me.
Don't forget the 48% barrier damage bonus, too. For Descent and Trespasser, that's pretty valuable.
They're all good. If you prefer crit damage, Lovias is better. If you like the party-wide effects of Encore, go for that. Or take all three and switch them up. You wouldn't want this staff in JoH, though.
But for a RM/Winter's Ruin build, I think this staff is right up there with the best. Nice find, phish.
Of course, getting it ain't all that easy. The other two are much easier to get.