“Purity rings” are more of an evangelical Protestant thing. i find them a little creepy because I don’t think a young person, usually a teenager, should be put in a position of making a public commitment in front of their peers about a sensitive and private topic. If any of those young people should make a mistake later, which inevitably some of them will as we are all imperfect humans and sinners and sex drive is a hard thing to learn to control. then they’re in a position of trying to decide whether to take off the ring, thus putting their mistake/ sin on public display, or keep wearing the ring though it may be a bit hypocritical.
If someone wishes to make a personal and private commitment to chastity, and wear some Catholic item to remind them of it, like a ring, medal or scapular, then fine. Do it privately and it’s between you and God, not a big show of purity that you’re putting on for the world.
I agree that if you want to learn about chastity and purity, it’s better to learn from Catholic resources. However, I note that many if not most of the Catholic resources other than the Catechism and “Theology of the Body” (both of which are good, don’t get me wrong) are directed at either males trying to kick a porn habit, or gay people. There isn’t much out there to help normal young women with their chastity.