Through the above website, I sent a few questions regarding the unit and that is when they came back with the 3 device comment, which is what confused me (as I had the same understanding - up to 6 riders). The 3 devices may be independent of the rider connections though. That is what I am trying to figure out.
Anyway - the device looks like it has promise and am interested to hear your thoughts.
I think I know what confused you - the 3 devices probably refer to the F5's ability to connect to three different BT devices such as a smart phone, GPS and media player.
The 3 devices seem to be independent of the rider count.
In fact, the user manual states that any number of riders (intercoms) can connect, but 4 is the optimal, and the sound quality degrades with more connected intercoms. Looking at the rider diagram (400m between each rider) it is highly likely that intercoms acts as relays to each other, passing the messages along.
I think the F5 is a device with 4 internal BT modules - three for non-intercom BT devices and one for BT intercom, and the BT intercom devices competes for a time slot on the bandwidth.
That can explain the comment on infinite number of intercoms and also the degrading audio quality; a behavior expected when several communication devices compete on a limited bandwidth (reminds me of the Networking course I studied in University when learning Computer Science; I wonder what algorithm is used inside..)