The short answer
Professional and Enterprise both give the team one shared credit pool, funded by the plan's monthly credits. Owners, administrators, and members spend from it. Professional allows up to 5 members, the owner included; Enterprise has no member limit. Unlike RFEM, CALC is not licensed by concurrent users. Each member signs in with a personal account, and all members can work at the same time. Accounts must not be shared. When Mia works in RFEM, your RFEM license terms still apply.