There are two different aspects there: full duplex communication vs mesh networking.
Most mid-level helmet systems should allow three users or more, each with full duplex (i.e. receiving and transmitting audio at the same time) capability. E.g. with Cardo, a set of Freecom 4s should allow up to 4 users to speak together. The downside is that you're still just on a Bluetooth audio-over-data pairing, which means a very limited range (if you're in front, you'd better still be in range of the last guy at the back of your group) and frequent disconnections/trouble with reconnecting if you get too far from each other. This is why in practice, low- and midrange systems are good at talking to the phone in your pocket, your passenger, and MAYBE the guy in the lane next to you.
Then there's mesh communication, which is on the top end systems (Sena 20S and 30K, Cardo Packtalk and its variants). This means each helmet system is also a retransmitter for everyone else in the chain. So you only need to stay in range of the next guy, and he needs to be in range of you and the guy behind him - and everyone can hear everyone. These systems are also better at reconnecting those that have dropped out.
But (speaking as a moto marshal for bicycle races), when communication is REALLY important, the best system is still a bodyguard-style earpiece with a PMR/walkie-talkie type radio. Cumbersome but far more reliable, and cheap.
|