This item is meant to be a magic equivalent to a vanguard. It is effective at blocking damage from DoT spells in small/regular instances and less effective against a bigger burst of magic damage. Note though, that it does not provide Damage Block, but a regenerative barrier. so it can be overcome by multiple sources of damage unlike a Vanguard. Ex: If you have 1 unit hitting a hero with Vanguard for 25 damage per second, the Damage Block will absorb it and reduce the damage to 0. If you up that to 1 unit hitting for 25 every 0.5 seconds or 2 units hitting for 25 damage each, the result is still the same since the Vanguard blocks damage from each instance. Whereas for this item, if you have one spell dealing 25 DPS (after reductions) it will be blocked by the passive regen of the barrier ability. If you add another 25 DPS ability on top of it though, that will not be mitigated by the passive barrier regen.