Personally, I have had an automatic door for about 3 yrs now and love it. Like you, I wanted one for those times when we might be out late and didn't want to worry about the girls being locked up. We have never had a problem with anyone being locked out as we make sure to change the opening and closing time as the days get longer. Some have a photo sensor, but since our coop is at the edge of the woods that option didn't work well for us.
We have the Pullet-shut automatic door and actually have it on our secure run instead of the coop. Since the coop opens into the secure run, we only close the coop door during cold winter months. So the chickens hang out in the secure run until the auto door opens into another run which is only partially covered. Even though I got it mainly for night time close up, it's also nice on those mornings when I enjoy a few extra minutes of sleep as our chickens get up very early.