The Unmaker is a tier 2 epic Two-Handed Hacking weapon. It is preceded by the tier 1 epic, Earthquaker.
Void Core: 22
Max Level: 75
Max Att: 225 (+3 / lvl)
Max Def: 37 (+0.5 / lvl)
Max Dmg: 300 (+4 / lvl)
In general, this weapon is better for tower attacks but not as a defender for a few reasons.
First, it does not benefit from Raging Shout. Raging Shout is a damage buff skill crucial to the Berserker's damage, as it adds a whopping +125% additional damage at skill level 10. Damage buffs do not interact with non-physical weapon damage. This makes it less ideal for tower defense, but it will also rely less on active skills making it ideal for tower attacks, where Chill Turrets make damage outside of soul skills almost worthless.
Second, against enemy heroes, a Berserker's greatest asset is his ability to deal area physical damage on demand, with high numbers due to being a damage-dealer class. Upgrading to this weapon will turn the Berserker from a physical damage dealer to an elemental damage dealer similar to a Warlock, except with a much stronger self heal and high crit chance. This will hurt his role in tower defense, but since most defending machines and monsters have low shadow resistance, his soul skill will become one of the most useful for clearing tower floors.
For all these reasons, The Unmaker may not surpass lower-tier alternatives until max level or near to it, unless you spend too much on the weapon to maximize its level and enchantments, so this weapon can actually apply massive damage to your opponents without the need to apply a buff on the Berserker. This is a considerable investment to keep in mind when one is debating which tier 2 epics to prioritize crafting.
On the Battle Priest this weapon is generally not ideal since it does not provide defensive boosts and does not deal light damage, which is important for him. However, his vengeful fury skill will apply the full shadow damage to all enemies regardless of how many there are, but it is still outclassed by the Prelates Justice.