Great against single large targets (bosses) as the Destroyers will immediately gravitate toward the enemy and explode all at once, doing massive damage.
Against larger mobs of weaker enemies, Destroyers often unneccessarily gang up and explode on a single enemy, but the radius of their explosion may still be enough to kill nearby opponents.
Destroyers will self-destruct at the end of their duration if they weren't able to find an enemy to attack.
Choosing the Endurance modifications allows the Destroyers more time to roam around and seek out other targets before they self-destruct, but they will not follow the Dragon Mage. These two mods can safely be ignored in favor of Bronze mod Explosive and Silver mod Swarm. More Destroyers can always be summoned, so increased life is not very useful compared to increased damage. For Gold mod, either choice is excellent.