Bluetooth over certain frequencies can be several hundred meters.
Bluetooth is only specified for the 2.4 GHz band. Class 1 (20 dBm Tx power) will link reliably well over 100 metres in line of sight applications with suitable antennas, but helmet mounted or embedded that is unlikely to be achieved, particularly on undulating terrain.
I don’t think the inter-helmet comms are Bluetooth. My guess is WiFi, possibly at 900 MHz, since the Sena blurb talks about 9 channels being available. Bluetooth uses frequency hopping across the entire band while many WiFi implementations are more channelised. Channel bonding is unlikely to be needed for the bandwidths required for low latency voice traffic.
If my guess about the WiFi spectrum is correct the product is unlikely to be legal to use in the UK.
As a non RF nerd point, and as others have said, if you believe that a helmet will protect your head in a crash, why would you insert a lithium battery, PCB and sharp metal connectors in the polystyrene?