Question about Cardo Freecom 4x Duo

Yes, that works. The coupling 'must' be done like a chain circuit, as a 4x 'only' has 2 IC channels. As 5011wireless has written, this also serves the range.

This has to do with the type of connection. The chain you have seen describes the connection of the devices via Bluetooth. You must select this type of connection if you want to connect Sena and Cardo with each other. However, if you only want to connect Cardo devices to each other, you can use the mesh function. This works like a network. Everyone can leave and come back whenever they want. With the Freecom 4x, up to 4 people can be connected to the network. With the Bluetooth connection also up to 4, but with lower quality and range. Hope this has helped you. LG McFrisli

Yes, they can all communicate with each other: Chain = each device 2 channels e.g. driver1 A/B, driver2 B/A, driver3 A/B, driver4 B/A.
The best result is when the sequence remains constant during the journey, e.g. if Driver3 is travelling quickly, there are interruptions that sometimes resolve themselves automatically, but I have also had to re-dial/call in order to have contact with everyone again.
But contact is good and clear,

Tip: reload/update the firmware with the Cardo Update App on the PC, brought a significant improvement (depending on age and version), it is best if all devices are running the identical version.

Yes, they can all communicate with each other. The "chain" is used for transmission over longer distances.