What's the best way for parents to monitor Instagram secretly?

I’ve been in a similar situation, not with a kid, but with someone I care about, and I’m still on the fence about using monitoring tools - it feels like an invasion of privacy, but at the same time, I want to know what’s going on. I’ve heard of apps like Eyezy, but I’m not sure if they’re reliable or if they can be detected. Has anyone had any experience with these kinds of tools?