Except that you have to be invited to join. Weren’t you aware of that?
I had a friend in Opus Dei. Never any mention of being invited to join.
The only thing I didn't like about it was that she didn't have as much time to hang out, shop, do lunch as before because the requirements of Opus Dei took so much of her time. Praying, Adoration, Daily Mass-those works of God things.
Though I was glad for the peace, holiness, and order it brought into her life, I, being a selfish jerk was not happy that it took time from our friendship and all the gossipy, running around stuff that was replaced by Opus Dei.
Are you sure?
Most/all stuff that Opus Dei does, in my experience, is open to anyone who shows up, and in fact, most of the people I know who are involved have no formal, official relationship to Opus Dei.
Anyone who wants to go to a retreat can sign up. Anyone who shows up at holy hour is welcomed. Etc.
Someone has to be "invited" to be a supernumerary in the same way and sense that someone has to be "invited" to join a religious order. It's a vocation discernment process.