I've been thinking about encryption all the way up to the display module, though, meaning interception would have to be very close to the display hardware itself.
We're also selling a premium package, where the device is much bigger but includes a physical display and keyboard, with a transfer mechanism of the final encrypted message.
We're marking up the higher end model so we can fund the lower end model, being 2 replacements of the dongle for 1 purchase, as the dongle will have a one time authentication and will be locked to the device.
We're also trying to figure out how to have the device self destruct if not used by any approved devices, meaning whipe itself clean and POSSIBLY break the hardware that does the processing/houses any data.