The big difference between ECMS1 and CMNA is the audience that it is geared towards. CMNA is a pre-sales focused course, so we spend more time going through individual products, features and deployment scenarios.
ECMS1 is an operators based course, so the focus is going to be on practical use and implementation. From a lab perspective, ECMS1 features some work around troubleshooting, which you do not receive during CMNA.
Overall, the courses do have some overlap, the differentiating feature is if you are going to be focused on design vs implementation/support.