Yapalong 4000 (5-User) Complete Set

We've used the eartec sets before that claim they are full duplex, but are not as good as the Ref-Comm Yapalong. The best part is that you can have multiple people with the open mic, or have one open mic and the rest push to talk (PTT). Not only that, everyone can hear when someone talks, not just a "slave" radio talking only to the "master."
When the referees are getting evaluated, the referee coach doesn't JUST want to hear the main ref, but also the assistant referee's on the sidelines.
If necessary for someone to listen only, you can hook up regular headphones to the radio, or an aux cord to a speaker, and not have the mic connected.
Another thing we like is that unlimited radios can listen in, not just 2 or 3.
There is some occasional interference, but that is to be expected and almost unavoidable. But there are things you can do to avoid that. Don't put the radios close together. Turn off other electronics or keep them away from the radios. Use the radios in open spaces with clear line of sight.

I owned Ref-Talk2 (the open mic version of RefTalk 1 I guess) and I didn't like their radios and static so I switched to Ref-Comm. Boy, what a difference. Thank you!