Why I don’t recommend Signal to my friends
I have two main gripes with Signal:

First, it’s only on mobile. I want something on desktop too, because I don’t see a reason to awkwardly type on a smartphone if I’m in front of a PC anyway (which I am most of the time). They do have a kind of desktop client they’re working on, but it’s a Chrome app and connects with your Android phone. I want something I can use to communicate even without my phone, not to mention a solution which doesn’t lock me into a specific browser. Update 2017-04-26: You don’t need Chrome running in order to use it. Still, I’d still like not to be forced to install software I’m not using.

Second, Signal’s SMS/web identity crisis is not particularly user friendly. “Hey, why isn’t my secure SMS delivered”, I hear the potential users yelling before heading back to the warm embrace of Facebook Messenger. The question of an SMS fallback has been discussed several times on the Signal issue tracker; see #3220 and referenced issues for more information on why we won’t see it.