As with most duress mechanisms, one would have to judge whether using it was better or worse than not -- I suppose ideally one would have two, one of which simp

As with most duress mechanisms, one would have to judge whether using it was better or worse than not -- I suppose ideally one would have two, one of which simply reenabled the passcode and would have some deniability (this is effectively already possible by using a nonstandard finger, unless LE has witnessed previous successful unlocks and can identify the finger which should be used), and one which initiated a wipe of the phone.