Smartphones have so many problems with them, I really wouldn't feel
   'secure' using anything built on top of a smartphone. From the baseband
   to the OS, there's been a lot of yellow and red flags raised around
   smartphones. Even a well-audited app I would still be cautious around.
   There may be nothing wrong with the app itself but I simply don't trust
   the platform. Smartphones are many steps at multiple layers from being
   secure.