As a brooder coop, I think that is sufficient, and I would keep that set up if possible. But that is because I recently got my second coop/run, and it is so handy. While it is working now, with 10 week old birds, I too, do not think it will be enough space for full size birds. Many times people post on here, that they have a flock of birds raised with each other, that have always gotten along just perfectly in their set up, and now are getting some very ugly habits, with bullies and victims. What has changed is the size of the birds, a coop that was sufficient space, is no longer enough space as each bird is bigger. So while I think that they are getting along well now, I think it might change.
People often think that free ranging or run space can make up for not enough coop space. And even I have cheated a bit in the summer. However, the days are long in the summer and the nights are short. In the winter, my birds are roosting up by 4:30, and staying on those roosts until 7:30. That is a long time to be cramped for space. In the winter, I believe, one needs to measure their coop, and cull their flock to fit it.
As to your original question, I never lock my birds up, they can go in or outside as they want. I do have a mostly predator proof ( recently tested, found wanting, corrected and awaiting further testing) run.
Mrs K
