I don't believe in those wrist guards. You'll just end up breaking your arm above where the wrist guard stops anyway. My friends wife wore them, and well, she did just that, broke her wrist above where her wrist guard stopped. Just practice falling with your fists closed IMO.
A fracture through the mid-radius/ulna has a much better prognosis than a wrist fracture. If you're hitting with enough force to break something, not much is going to prevent it from happening - this will at least make it easier to heal.