Your comment on image is possibly also true. I remember much of the press of another messenging app oriented toward privacy came because it advertised as "the beautiful messenger" with many nice pictures. It was Icelandic with .is site but I don't recall name. Versus competition, wasn't much to say in terms of implemented features or security. The U.I. was beautiful, though. ;)

Note: The Apple website takes this technique about as far as it can go outside a dedicated, high-def, image board.

Note 2: I could add Nim to my prior list if there's been any work evaluating it for security-critical applications. Particularly, how it helps or hinders expressing such things plus risk compiler brings in during transformations. Anything on that yet?