there's no assurance that you're going to earn more money from bitcoins because you invested them. There's no 100% sure profit in investing no matter which platform that is or no matter what company that is. Investing is risky.
Indeed, the best opting is to just save it, because why would you want to risk your hard earned money in some site that is not going to give that much of a profit and may take it without giving it back, you are better off saving some of your real job and buying bitcoin and saving it for the future.