Basic biometric functions are supported very easily. Level 2 allows developers to utilize the biometric devices' more sophisticated functions.
Programming is slightly more difficult, but greater flexibility is available.
Level 1 allows for very specific and low-level device programming access, to utilize features which are specific to a particular device. In fact, the fourth layer could also provide HA-API compatibility. When a developer is assigned a task to integrate biometrics into an existing application, he is usually given this task as a potential feature enhancement. Up to now, many developers have had a difficult time selecting a biometric technology and device to integrate. Since BAPI addresses these compatibility issues, the remaining issue becomes whether or not to implement biometrics as an official design project.