It's for those who don't feel secure about their computers (travelers, paranoiacs...) or need to be 100% sure nobody can read their messages.
So all of them would have to trust and buy your ''device' 'that is ''100%'' safe?
It's much easier to use some open source software that would do the same thing than to use some device that can have backdoors, hidden code and can be affected by supply chain attack.