Only for morons is way harsher than I'd put it, but fundamentally it's a difficult to inspect security system that's based on a potentially vague analog signal.

Only for morons is way harsher than I'd put it, but fundamentally it's a difficult to inspect security system that's based on a potentially vague analog signal. In the security world, things which are novel are not to be trusted. The security of a system is measured in how many serious researches have attacked it, and to what degree they succeeded. I expect that there are solid biometric security standards that have been subject of serious analysis and attack. If it turns out that Apple's implementation uses one of these standard and tested solutions then I think I'd trust it in place of a PIN. In the absence of that evidence, the Properly Paranoid position is the skeptical one. A quote from Babbage in 1864 is apropos: "One of the most singular characteristics of the art of deciphering is the strong conviction possessed by every person, even moderately acquainted with it, that he is able to construct a cipher which nobody else can decipher."