The problem with Signal (at least for me) is that its desktop client relies on your phone's Signal app, which feels weird and "duct tape-ish". I've been spoiled by the ease of using iMessage with multiple devices (phone, tablet, desktop, or otherwise): just sign in and it works, no janky-feeling interdevice communication necessary, and I've come to expect that from any messaging service I use.

Signal is great for those who confine their instant-message-like communication to their phones, since desktops being treated as second class citizens isn't an issue for them. I am not one of those individuals. I want to be able to read and reply to messages on whichever device I'm using at the moment without having to think about my phone's presence at all.