To maintain your payout a cloud miner would have to spend thousands extra to buy more machines and electricity to combat difficulty changes.
Are they going to do that? It would be dead nice of them if they did but I'll go for a no.
Most cloud mining services run with a fixed hash rate or with a machine.
When you buy on some bullshit cloud mining service like Genesis Mining, they give you contracts to buy X number of MH/s, GH/s or TH/s. With Hashnest, you buy the machine's hashrate and the fees they charge are maintenance costs.
With some crazy crypto rallies preceding you buying the contract, I would say that it'll be completely shit within a month or two. Regardless, Genesis Mining is a load of crap and within a few months they'll be charging you more than the amount you earn. Considering that they try to hide how much they actually charge, you'll probably end up losing a lot of money in a very irritating and complex process.
tl;dr: just buy.