Every Broker which offers the cTrader Suite also offers cMirror, whether they advertise it or not. While every cTrader broker supports cMirror some of them may offer a limited service because of the type of subscription they have with Spotware.
Here are the different type of subscription which your broker may have:
cMirror is completely broker agnostic and the broker that your Signal Provider(s) use is an irrelevant factor to latency or performance of their strategy.
As different brokers may have different pricing structures it is possible that there may be some differences in charges, if this is a concern to you we advise you to review your Signal Providers charges to understand what charges they have incurred and how they compare to yours.
Definitely, you use your cTrader ID to access cMirror, not your Broker’s log in, you can link as many different accounts to your cTrader ID, regardless of which broker they are with or whether they are Live or Demo.
In this case those trades which use unavailable symbols will be disregarded and nothing will be done in the Mirror Traders account, simply those trades will be skipped.