As many have already indicated, it's not mandatory for regulatory purpose but may be necessary for sales.
In choosing an NRTL (UL, TUVs, ETL CSA etc), you might quiz the NRTL on how they plan to handle the 3rd edition and requirements outside of OSHA's scope.
The NRTL rules are limited to occupational health and safety (i.e. workers in the health care environment, not the patient). Modern standards for medical devices have expanded far (far) beyond this scope, so it is important for NRTLs to set a reasonable boundary for their mark. Each NRTL will set their own policy, this policy will determine how expensive and complicated compliance testing and factory inspections will be.
Quiz the NRTL on this point. If they say they plan to limit to "basic safety" only (shock/fire/mechanical), sounds like a good NRTL. But make sure thier quotes, scope of tests and fees reflect this policy.
If they say they want to test everything, run away.
If they don't understand the question, run away.
And worst, if they quote and charge you to test everything but their reports quietly have a disclaimer on page 3 saying they only take responsibility for basic safety (yes, you know who you are ...), run away.