Comparing position on Update or using camera visibility?

Hello ^^
I have a game where some couroutines start when their game objects are in the field of the camera which follows the player.

Will it be better if I compare the distance between the camera and the object to start those or should I just stick to OnbecameVisible/Invisible?

Thank you ^^

Create a Trigger (Sphere?), put it as child of the cam and use Trigger Events.
With OnTriggerEnter + OnTriggerExit you can activate / deactivate the desired state of the Intruders.