The RDT-CFNC-0200ASE is a service entrance rated model and can be installed between the meter and main to meet code requirements.
The RDT-CFNC-0200A is not a service entrance rated model and is typically used to power a subpanel or if used in whole house application a separate service entrance switch is required.
Please consult with your installing electrician as to which switch would work best for your specific application.