For the first two, based on personal experience:
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Anecdotally, my old back-mounted LG fingerprint scanner has never been wrong (when dry of course), but my Pixel needs a re-scan 30% of the time.
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My phone requires a tap to wake the screen before the fingerprint reader will accept any input at all, unless I decide to burn battery and turn on AOD.
E: My current phone uses an optical sensor and, from what I understand, ultrasonics are infinitely better
I think Stealth on FDroid combines Reddit and Lemmy, but I don't really use it much or mess with Reddit anymore...