Why on earth would anyone choose to use Android or indeed any Linux-based OS to do what they want to offer? If they want to build a phone that is completely locked down, Linux is way too bloated for this. The only reason that I can think of that they chose Android would be to take short cuts. If they think they can produce a secure phone simply by stripping out Google services, preventing the user from installing anything and by adding encryption, they are very much mistaken.