Once you are on the internet connectivity there is nothing private or secure anywhere and by anyone no matter how much they claim,if you have something personal then keep it away from online services always
Safe as in what sense? See if you're trying to send on some nuclear missile codes over anything on internet then it's not safe.. but like if you do personal chats, then it's absolutely safe, no worries. To state it more clearly, RCS is as safe as your SMS were.
