I feel like this is why Hovding says it's "not intended for people under the age of 15". It's not that it wouldn't work most of the time, if not "all but a single time" and are simply protecting themselves from a possible lawsuit.

What's to prevent a condom-like "99% success rate" as legal backing for "haha can't sue us if it fails because we didn't promise 100% success rate"? Even though, effectively and when used properly, they have a 100% success rate... it's just there for legal reasons to prevent lawsuits.

[0] http://www.hovding.com/