Seems like it's not tested well. I updated to Signal 2.0 on an iPhone 6 with the latest iOS 8.x. It said that none of my contacts have Signal (that's true) and had a link titled "Invite your friends". Tapping on that took me to the home screen. Killed it and tried a few more times. No use. If it were as usable as Telegram, I'd insist my contacts to switch. But not right now.