I think I was in the 7th or 8th grade when I first heard about purity rings. Even at my very naive age, I thought they were complete bullshit. Really? I thought, you need a ring to remind yourself to not lose your virginity? I found the whole notion quite silly. Remaining pure till after marriage is a commitment you make to yourself; wearing a purity ring broadcasts your decision, and it becomes more a commitment to the public rather than one to yourself.
Purity rings cause a problem to the wearer who changes his/her mind. Our mindset and decisions and priorities are altered, even if just a tiny bit, on a daily basis. Suppose you meet someone and decide to go ahead and have sex with them: you must take off your ring first. Suddenly, the public eye is focused on your ring finger and its lack of a ring!
In summation, I believe that a commitment does not need a ring, it only needs a determined mind.
Just felt like sharing an opinion.