The true test of any biometrics technology is not how it behaves in the lab or how it behaves under ideal conditions, but how it performs in the real world. For many years now, the promise of biometrics has not been fully realized in large part because performance in the lab is not representative of performance in the field.
When biometrics fail, for whatever reason, the technology becomes more of a barrier than an aide. The net result is user frustration, resistance to adoption, and an inability to justify costs. Regardless of which biometric technology is chosen, it must work reliably under real world conditions. The real world is not always ideal. The real world is wet, it is dry, it is not always clean and users are not all young office workers with great skin experienced at using the technology.