The C-4 used an external Zigbee + ZWave USB stick. We'll ignore the C-4 because you don't have one, and swapping is trivial. 
However, the C-4 taught us that adding a 2nd ZStick would allow that 2nd stick to become the ONLY ZWave radio. This is still how Hubitat ships Hubs to non-USA frequency locations.
Yes, buy both.
While you're waiting for delivery, build a computer to run either ZenTools or OZWCP. ZenTools is a windows program and I have successfully built a working one via a Virtual PC (VirtualBox on my Mac.) OZWCP (Open ZWave Control Panel) runs on many platforms, rPi is popular.
Both tools are low level Stick only tools to allow you to manipulate a ZWave stick and it's contents. You begin by clearing it if it isn't already and joining your Hubitat ZWave network as a 'secondary controller.' That process causes the 'primary controller' inside Hubitat to send it's entire DB of Z-devices to the 'secondary controller' and thus you've duplicated the internal 'stick'. Aeon distributes a backup tool (windows only) and you close ZenTools and start the Aeon tool and you have a disk copy of the Hubitat ZWave stick's DB of devices. The Aeon ZStick still has a copy, it's good to go, but if the first step is clear it, and the 'join as secondary' fails, you have nothing.
If the HUB dies, with the internal ZWave radio component (stick) gone too.. then when you get the replacement hub, you plug it in, register it, and restore your backup of the Hub's DB (related to the stick's DB but NOT the same.) Then you cable up the Aeon Zstick with its backup and you should be off to the races.
