can u link which one you use?
Automatic opener for flap door? - Page 3
We got ours because the getting up at sunrise every morning was getting old...especially if it was cold or raining. A couple years of that (bathrobe and wet/cold crocs on my feet) and for us it's been money very well spent!
Here's where we got ours:
It runs on a 6v lantern battery and is supposed to last 6 months to a year. I got rechargeable 6v's and swap them out every 3 months. We've never had a bird get left out (they usually go in about 1/2 an hour before the door closes. This door also has a "reverse" feature so if a bird were to get in it while the door was closing it would go back up just like a garage door would. Ours has been working for 6 months now, without a single issue. If you're worried about birds not going in, there are several modes which will open the door earlier and close later based on what you need. All the info is on the site.
It doesn't even take 5 minutes, but sometimes I get home late due to running kids to activities and it is open an hour or two after dark. For example, tonight is trick or treating. My girls will not go in until good and ready, so if we leave before they go in, the door will be open after dark till we head home.
For me it will be piece of mind knowing if I am running late they will be safe.