Usually when I see smart people talking about security, they think about what attack vector/situation you are trying to protect against. In this case, the situation you are trying to protect against is not keeping your phone locked when you are in custody or at gun point. The situation is someone unlocking your phone if someone swipes it from your pocket, you lose your phone, or simply leave it on your desk for a few moments as you go to the bathroom at the office. So, yes, a biometric scanner, even one that is easily beaten by an attacker, is good for this purpose.

Whatever the case, maybe we should step back and get some more perspective. How many of us don't put locks on our shared computers and phones because we don't want the inconvenience of ensuring everybody that should be allowed to use it can? My phone is a shared device and I removed any and all locks on it as I got very tired of "oh, let me unlock that for you." Basically, I want everybody that can reach it physically (when it isn't lost or stolen) to be able to access it and make calls, surf the web, use the map, search contacts, play games, etc. Is any phone locking mechanism going to work perfectly, probably not. Being able to set up my phone to unlock for anybody in my family and friends circle by something like fingerprints is a pretty good start.