BLY, I work at ACR Electronics and can answer your question. The McMurdo product is approved as a PLB. By regulation an EPIRB and a PLB have different performance characteristics. Here is a partial list below. EPIRBs float in an upright position to transmit (perform best when floating) PLBs float so they won’t get lost, some need pouch to float. (They need to be held out of the water or attached high up on PFD for best transmission) EPIRBs transmit for 48hrs at temps down to -40C or -20C (Longer in nominal temps) PLBs transmit for 24 hrs at temps down to -20C (Longer in nominal temps) EPIRBs can be manually activated in or out of their bracket or automatically activated when out of the bracket and in the water PLBs are manually activated EPIRBs have a strobe light PLBs have no strobe (some newer versions have flashing LEDs) EPIRBs are designed to be mounted in a bracket or carried in a ditch bag PLBs are designed to be worn or carried on your persons EPIRBs are registered to the vessel PLBs are registered to the person and are legal to be used on land as well Both are required to be registered with NOAA. It’s quick, easy and free and can be done online at http://www.beaconregistration.noaa.gov/ I hope this is helpful. Stay Safe Chris