Almost exchange right now needed KYC and become more security for your assets saving, you can hold for long time your coin on the exchange market without worry with your account after success submit KYC, but CEX.io is not guarantee you will hold safety your coin there for long time because many exchange have been stop working after their exchange hacker and without give back for investor money although billion dollar their coin assets in exchange market.
Each exchange has its rules stipulated that you deposit your funds at your own risk. If the funds are lost, stolen by hackers, they will not be refunded to you. This rule applies regardless of whether you are going through identity verification or not. So keeping your assets on exchange wallets is not safe.
It's true that every exchange has its own rules like Kucoin which was hacked yesterday but Kucoin guarantees the safety of funds for its users because they have insurance if something happens like this, but all exchanges can't do this so please keep assets on the exchange not too long because it's a high risk.
No matter how strong the security is applied on the exchange, hackers will definitely find loopholes to take the money.