That said, I have an iPhone5 without fingerprint sensor, and if I get a version with the sensor, I’m not going to use it. I don’t trust such a sensor to always recognize my fingerprint in an emergency, which is the reverse problem. :-)
The phone can always be unlocked with the passcode. The "fingerprint" is merely a convenience (or to use with ApplePay) for quick access. The option to use the passcode is not locked out if you activate the TouchID. I have found that the TouchID is only finicky when the temperatures of my fingers are too cold, or my fingers are wet. Otherwise, it is 100% responsive. I have three fingers coded to unlock my devices and they all work, but the uncoded fingers will not.
On the other hand, a friend had a Motorola with a fingerprint reader and it was only about 30% reliable in reading her fingerprint. . . that phone required you swiped your finger along a reader of some kind as I recall and she was always swiping multiple times until it would finally unlock. Funny thing was, although my finger was not programed in, it would also unlock to my finger after about four or five swipes. LOL!