I have Nexus 7 and Samsung Note 4. I'm guessing that they are representative of Nexus and Samsung Android devices, respectively. Regarding full disk encryption,
Nexus full disk encryption is irreversible (unless of course you do a factory reset), but Samsung has an option for decryption.
After encryption, Nexus can be unlocked by any option (including a simple screen swipe without password), but Samsung requires either password or fingerprint. Is there that much use to encryption without password or fingerprint to unlock?
What are the reasons for these strange differences?