Not sure that they work like helmets do. Helmets are designed for a "one 'n' done" type protection. Wrist guards are generally used over and over. Never heard of anybody getting new guards cuz they had a fall and didn't
break their wrist!
I expect you broke yours while wearing guards because they weren't designed to protect properly. I really can't speak to the medical or scientific accuracy of their claims, but I understand a lot guards aren't. (....that is if you believe the Level V marketing hype.)
I own a pair of their mitts, had them for 3.5 seasons. Although, nowadays, I fall so infrequently I'm just as prone to wear them without
the inserts as with.
Your biggest concern for proper protection is the right size and fit!!! Especially with second hand gloves. If you are fitted properly? I don't think you have anything to worry about, but if you are really concerned, I would suggest e-mailing the company and ask.