The big question is, not will it be a quality scanner, but will it be useful? I'm sure there are some people who will welcome the added security, but for 95% of folk, they will probably use it for a week and then go back to having a pin. It's superfluous technology for the majority of Iphone users and you are running the risk of having your fingers chopped off.
I'd say if it is a quality scanner - then it will be useful. Why would I want to type in my pin over and over if I could have the phone unlock at a single swipe (or even just the press itself?) of the thumb?
And my fingers will probably be safe from chopping at least until I become rich and famous