The effect of “Armed Changer” activates when the destroyed monster is sent to the Graveyard in the Damage Step. This effect can be chained to.
If the monster equipped with this card destroys a monster like “Sangan” or “Mystic Tomato”, its effect will form a chain with them according to the rules of simultaneous effects (see Advanced Gameplay FAQ).
If the monster equipped with this card destroys a monster with equal ATK, then its effect will not activate, since “Armed Changer” is sent to the Graveyard at the same time as the opponent’s monster.