Thank you. Yes, you are correct - using Android setprop is the official approach. The upside of this approach is that the user himself can enable verbose logging if so he wishes. However, I strongly believe that the official approach here is wrong, because:
1. it is annoying to enabling DEBUG via setprop every time I am going to develop, and disabling it afterwards.
2. when user enables verbose logging, he will be swarmed with debug messages from all other apps.
But, I believe that you are right and it is safe for the official slf4j-android to stay with the official approach; for those that do not wish to tinker with the setprop there is slf4j-handroid