Either will work well. I chose the timer because I'm a bit OCD, and want control over when the door opens and closes. Honestly, the light sensor does the exact same thing.
I've never had a hen locked out because of the automatic pop door. I set the timer to close the pop door 30 minutes after it gets dark and open it some time around dawn. I adjust the timer every month or so.
I let the hens free range quite a bit. One evening the wind blew the door to the run (NOT the pop door) closed and locked out all the hens. I usually check on them before heading to bed to close the door to the run and make sure everyone is accounted for, and found all the hens stacked up on a step ladder I had left next to the coop. If it had been daylight it would have made for a GREAT picture! I put them back in the coop, on a roost, and started using a brick to hold the run door open instead of a stick. All has been good ever since.
The automatic pop door keeps doing what it is supposed to do and the hens stay happy. I have a good measure of confidence the hens get closed off from predators each night. I also mosey out of the house on Saturday mornings to enjoy a cup of coffee on the back patio knowing the hens were let out on time, without my intervention. Life is good! Both the timer and the light sensor will get a person to that point. I really don't think there is a bad choice here. It kinda reminds me of: deep litter vs. shavings; crumbles vs. pellets; watering with nipples vs. cups; using 2x4s vs. branches for roosts; free range vs. cooped; poop board vs. poop hammock; and... and... you get the idea - choose one and make it work.