I think it is good to remember that security is situational. So unless a prisoner is holding a copy of every officer/guard/transfer agent's finger prints, they won't be able to undo the lock while in most detention situations (the only ones I can come up with are fairly contrived, or require the prisoner to escape in cuffs, making the point moot). Basically, if the arresting officer puts the cuffs on the detainee, and scans in his fingerprint as the "unlock with this fingerprint" option, it becomes very difficult for the detainee to get a copy of that print in a form that will work, and then use it, unlike an accessible hidden key known to work with $model-of-handcuff.

Of course that says nothing about other ways to defeat the cuffs, which would probably become the prime area of research at that point. (why attack the locking mechanism if there are easier to defeat weaknesses).