Opus Dei - what I should know about my new friends

I am a devout Catholic - and I love it. I am not looking for anyone to tell me otherwise haha. I am a cradle Catholic, however I returned to my faith about 4 years ago. I’m now married and have an infant son. My husband is devout also.
Recently, I’ve made some new friends who are part of Opus Dei. We met through a local play group. I knew nothing about Opus Dei and have never heard of them before. From what I’ve read it seems bad? These friends are very normal - I’ve been to their homes and they are normal too - nothing weird going on. The only ‘abnormal’ thing I guess by today’s standards is that they all have a lot of kids, like 10 kids! Other than that there are 0 red flags. We have general discussions about God, our faith and prayer life etc, but it’s the same conversations I’d have with any Catholic. They have sent me information about a retreat, but when I declined as I don’t wanna be away from my son there was complete acceptance and no pushing.

I guess I’m here to ask if anyone has any personal experiences with Opus Dei members? These friends are really nice and I love that my son is around other devout Catholic kids!