Is it safe to use Android KeyStore Provider?

Question

Android

Task: the application must store the secret key (string), securely, without the possibility of extraction through decompilation of the application or root.
It is known that Android has three built-in mechanisms for storing secret data. KeyStore, KeyChain and Android KeyStore Provider:

• KeyStore is the least secure (because you can get access directly to the file with encrypted data using root)
  
• KeyChain is more convenient for sharing secret data between applications (asks user for permission via system dialog)
  
• Android KeyStore Provider seems to be the most suitable for the task.
  

Questions:

1. How is the Android KeyStore Provider protected from application decompilation?
   
2. Can we avoid the destruction of information when changing or disabling the password to the device? Android 6.0 and above.
   
3. How is Android KeyStore Provider secured on rooted devices? It seems that on some devices a certain hardware-protected storage is allocated for storing such data, where access is denied even with root. But what are these devices? How many? And what happens on other rooted devices - is this data just in some directory?