I'm a bit late catching up with this thread, but in case anyone finds it in the future, I thought I'd share my experience.
I've had a VSB since I first started keeping hens, as I used to leave home before dawn in the winter & get home after dark. In that time my VSB has had to be sent back for repair twice. It's one thing if the batteries just go flat (though there's no way of telling), but I was upset when the unit failed & the girls were shut in. If I'd been away for the weekend with no-one to look in on them, they'd have died of dehydration.
If I were buying another door opener I'd again opt for one with a light sensor, but a model with a four year warranty sounds more reliable. Never depend on the door opener 100%; do be sure to check on it. It just saves you from getting up do early.