Ive always thought of the chicken tractor as a device to house chickens in summer and fall that are destined to become roasting birds. Meat birds.
There is no reason why egg layers cant also be raised in a tractor. But for the limited space of my back yard, a permanent coop and run for the egg laying hens makes the most sense. That leaves room for the veggies gardens, fruit trees and berries.
I have foxes, skunks, raccoons and bears that regularly enter my backyard spring, summer and fall.
I would feel less loss if a predator got a few juvenile meat birds rather than my main eggs layers.
I plan on making a tractor soon. But, I have not seen any tractor design that is as secure as my coop and run.
So if your main objective is eggs, and if predators are a big issue, go for a permanent coop and run.