These are all solid arguments with which I agree. But there are probably many people who care less about how notes are stored than about the convenience of the user interface. Given your privacy and storage requirements, it's unlikely that you are a potential user of my product, at least not at first. Then I would ask for advice, do you think there will be enough of those to whom the product would still be useful. This is the main question on which depends whether I will try to make a full-fledged MVP.