The problem with that approach (for most folks) is that the open/close times won't change as the seasons change. A real pain to go out and reprogram it for changing daylight hours. Looks like the PulletShut people have finally added a photo sensor attachment (cabled) to their product. I think they were getting their sales hammered by the Ador1 which has a fully integrated photo sensor (no cable).
You should consider the Ador1 along with the PulletShut. The Ador1 has fully integrated and enclosed battery and photo sensor, batteries last for years, and the form factor is superior for most applications (opens vertically instead of swinging open). But your mileage may vary.
I looked at both doors very closely and it was a tough decision. There are things I like about each more than I like about the other. However like I said for myself the pullet shut door works better because I live in a neighborhood and I do not want the door opening at 5:30 when it gets light out. I have mine set to open at 8am this way the roosters crow is muffled inside the coop. The biggest downfall with the pullet shut door is the fact that you do have to go out there in the morning to set the opening time and again at night to set the closing time. However I will only have to do that 2 or 3 times a year so it is not that bad. When the days start getting longer in spring I set the door to close at 8:30pm and then when the days are short I will have it close at 6pm.