Just because they are using them doesn't mean they are allowed to, it just means they haven't been caught yet
They should only be used in competitions when they are used in every game, otherwise competition integrity can be compromised. Take a scenario where a team don't get a clear penalty because the referee is blocked off and it isn't credible for the AR to come in, there is no comms so he has no way of discreetly telling the referee it is a penalty. The following week the team that didn't get the penalty commit a foul in the same part of their own penalty area that the referee again doesn't see, but this time the AR informs him over comms that it is a penalty. Two identical situations but different outcomes due to having technology in use in one game but not the other.
The other problem at lower levels is credibility, you will stand out like a sore thumb as you will be the only referee wearing them. They will see a referee and his team with professional equipment that they are used to seeing on the TV so they will expect a better than normal performance, and if you don't deliver it they will be all over you, even more than usual. Not dissimilar to wearing badges that you haven't earned. You also open yourself to ridicule, I once watched a step 6 game where the officials wore comms, they were lining up in the tunnel before the game and one of the captains said "f*** me lads, the Backstreet Boys have let themselves go", you really don't want to be the subject of jokes before a ball has even been kicked.
Last but not least, you aren't trained to use them. When they were rolled out at higher levels the officials had practical training on using them, I was still a 3E when they got given to National League officials and was offered that training. If you don't know how to use them properly they can be more of a hindrance than a help.