She's a smart one with cat flaps, Rosella.
We didn't even show her ours, she just saw the others going in and out and decided she wanted to as well! (She had been here three weeks at that point.)
I have to admit, my partner was the same as your OH. He felt it would've been safe to let her out a week earlier, but I was paranoid as she wasn't chipped - the night before we got her chipped she made the decision for me!
Glad it's all "so far, so good!"