TL;DR: Stay away from cloud-mining. Most cloud-mining sites are scams, and the ones that are "legitimate" are money-losers.
Most cloud-mining sites are simple Ponzi schemes. You pay the site some money and they pretend to mine for a while, paying you a tiny amount every month. However, at some point, they simply disappear with the rest of your money.
There are a small number of legitimate cloud-mining sites scattered around the swamp of Ponzi schemes. The sad truth is that they are generally not profitable as investments, so calling them "legitimate" is being generous.
Let's look at it from the the operator's point of view:
You have a warehouse full of mining equipment and it is making a solid profit. Would you rent out this equipment for less than it earns? In other words, if your miners will earn 10 BTC, would you rent them out for 8 BTC and then hand your customers the 10 BTC? Cloud-mining operators are not motivated to make money for you because it is at their expense.
To demonstrate that cloud-mining is a money loser, look at the current situation with the well-known and "legitimate" cloud-mining provider HashFlare. They are terminating contracts because the maintenance fees are now more than the mining revenue, and the result is that customers have lost money.
http://fortune.com/2018/07/21/hashflare-shuts-down-bitcoin-mining/Many people believe that if the price of a bitcoin goes up, cloud-mining can be profitable, and that is true. However, given that the amount you pay for cloud-mining (in bitcoins) is generally more than you receive, it should be obvious that it is more profitable to just buy the bitcoins directly. It is also less risky.
