The free trial on the managed server is for a lifetime. So, there will be no fees on xCloud if you manage 1 site on one VPS server. However, your account will be automatically upgraded to the next tier when you add more servers.
During the trial of xCloud’s control panel, you get limited features. To use it, you need your own server, and you’ll have to cover the server costs. The trial is free for life until you add a payment method. You can also explore xCloud through the Playground during the trial.