Critical? not really. However it is very important to my organization. It helps us identify units operating at a scene, and even helps with accountability. Another department local to us had a FF go down at a working fire, his mic was damaged, RIT teams were able to figure out who it was and where he was operating by the Identifier. it not critical that it works on my G5 as it does work on all my other radios. That said its ability to display MDC was a major feature that was considered when the unit was purchased, may have opted for a different less expensive option if i knew that this didnt work. Its like buying a brand new car and having the glovebox light not work, is it critical? no. does the car still get you to wear you need to go? yes.. should it work anyway? yes....