Like Once. I can add a one time payment model, but installing it on a computer won't work. Because if the data is just stored on a computer: 1) it's not safe. 2) it's not reliable, the computer could stop working.

For one time payment, I agree I will need to implement that.

What feature do you think would be better for bringing trust to you and all users? Because I agree there could be a huge trust issue. I will encrypt the data, but would people trust it?