Signal's sub-par desktop app and "you can't restore more than five days of history and if you want more you're wrong" approach, together with the complete inability to use the normal app on more than one device (phone + tablet, for instance), makes for a pretty terrible user experience.

The protocol and the service behind it are state-of-the-art, but it's a tough sell if you're coming from something that just works on every device, like iMessage or WhatsApp.