Signal replaces your SMS app, which is good because it's perfectly seamless and there's no good reason not to use it, but bad because most conversations you have with it will be unencrypted because the other user doesn't have Signal installed. Unencrypted communications look pretty much the same as encrypted ones. The strategy is to eliminate inconvenience in order to increase takeup and challenge mass surveillance. But the tradeoff is that it's not such a great solution for an individual who really wants their comms to be secure.