I'm in the middle of building literally the exact same thing for myself.
Beyond privacy/security, the aspect of the app I worry about the most is giving oneself perfect memory and then never being able to escape the past. That last fight you had with your ex? Well now its recorded and you can listen to it, and dissect it, and wonder what you could have done differently, right up until you blow your brains out.
But, as always, its up to the user to use the technology in a healthy way. It would be, after all, a choice to remain mired in the past rather than taking healthy lessons from it to make your future better.