Fingerprint scanners are useless for security. My fingerprints are everywhete, especially all over my phone. Touch id merely buys time, which can increase security but if they get my fingerprints, make a dummy finger then they need very little time to open my phone. If they are determined they'll do it. If they are not, probably they won't care about the data in my phone.
They have at most 48 hours (or perhaps 24?) and 5 tries to find your fingerprint and unlock the device. TouchID will discard the keys and require a passphrase if it is not used for a while or after the fifth invalid fingerprint attempt. The window of opportunity is not that big. I would not characterize it as useless at all.
