Lower City Prayerbook
This item has a one minute cooldown. Because of this, using this trinket's cooldown whenever available can lead to an incredible amount of mana conservation. A Paladin will be able to cast Flash of Light nine times with this, resulting in 198 mana reduction. If they were to do this every minute, this trinket would provide a simulated 16.5mp5s effect.
Since this is not Unique, you can equip two of these purely for the extra +70 Healing bonus. However, both trinkets will share the same cooldown.