The first wave of vehicle to vehicle communicaations began with the introduction of the Citizen's Band Radio. It swept through the market like a tsunami. Even Harley-Davidson got into the act, installing CB radios or offering the option in their touring models & trikes. But over time CB has died a slow death, and Harley has de-emphasized it to the point that they no longer offer it as standard on any model. Yes, they stil offer the CB communications module, but the only antennas they offer are the Tour-Pack mount and a chassis mount that uses the old Dzus fastened saddlebag frame. (I had to fabricate a mounting plate for the H-D® CB antenna, but that's for another story.)
Let's get back to modern Bike to Bike (B2B) communications shall we? The next big step in B2B communications was Bluetooth. It grew out of the MP3 player market into bluetooth headphones, and finally into wireless Bluetooth B2B comms. Two of the biggest players in the market are Sena™ and Cardo™. Both have good Bluetooth B2B headsets. While their original Bluetooth is pretty good for short range communications, when the distance between riders starts to stretch out a bit it starts to have problems. Also, when you add more riders into the group the connections tend to become fragile. That's why I only recommend these original Bluetooth systems for groups of 1-3 riders. (Yes, I know the Manufacturers say 1-8 riders, but in the real world it comes down to 1-3 max.)
So what's the future of B2B communications? Mesh Networking is the future. Both Sena™ and Cardo™ have it in some of their headsets. Mesh can connect to up to 15 riders at a time. One of the Archilies heels of the original Bluetooth system is that it's a daisey-chain type of system, so if you have three riders, and the middle rider drops out, the daisey-chain is broken and the remaining two riders have to reestablish the link. With Mesh, if one rider drops out, the mesh automatically heals and continues - and if that rider reappears, they are automatically linked back into the mesh.
The problems with Mesh - right now there are two competing versions of Mesh networking, and they don't talk to each other. If your friends have Sena™, then you should buy Sena™. If your friends have Cardo™, then you should buy Cardo™. Right now, Harley only has Bluetooth headsets - no Mesh technology. Will they have Sena™ create an H-D® branded Mesh model in the near future? Rumor says that Harley will come out with their own branded 30K headset for 2019.
The whole thing boils down to what you want to do, how you ride, and who you ride with...