I think this is correct.
So a single activation can be the trigger for multiple effects, which all go off simultaneously.
If the activation only triggers one effect, which in turn triggers another, and so on, I would expect the effects to not go off simultaneously. Since the Hermetic 'clock tick' is Mom, I would expect at least that much time to elapse between effects that cascade in this way.
So we can have a device with three effects, the first a teleportation effect that teleports the device to a place the magus specifies (and to which he has an AC) during activation, the second an effect that creates a giant fireball and is triggered by the first effect going off, and a third effect that returns the device to the magus triggered by the second effect has gone off. Ok, maybe a fourth effect, to make the device extremely resistant to fire.
Of course, if the magus has an AC to some location, he can learn a fireball spell at AC range and just cast that. Or create a fireball item using AC range.