So yeah, it's a pretty fair pally weapon.A % chance of dealing Double Damage. The damage is doubled after all other bonuses, including elemental, Str or Dex modifying weapon damage.
Will never stack with Asn/Barb/Ama Critical Strike bonuses. It rolls for 2x damage for one, then the other if it fails. So having this increases double damage chances, but never allows 4x damage.