I used to be kind of indifferent to devices that let you flash your own firmware because I knew there was no way I'd ever bother writing firmware. But now the community is generating decent quality alternative firmwares for everything, devices having an unlocked bootloader could be a requirement going forward. If I buy an ereader in the future it will have to be fully unlocked so I can load whatever the latest community built firmware is.
but it's simply impossible to make a device which can keep a secret in presence of an attacker with physical access. It might be very hard but it's literally impossible, even embedded hardware keys can be extracted