When you start new disposable qube it’ll get extension from the caching qube.
IMO, the main security advantage of Qubes-Whonix, compared to using a locally running Tor service, is that it separates the gateway and the workstation.
In the guide you linked, the caching qube is sys-whonix, i.e. the actual downloading happens on the gateway itself. This completely eliminates the essential advantages of Whonix’s split-security model.
Well, I have 8 of them for different VPNs.
With the approach from the other thread, you would need as many downloading/caching gateways as the number of different VPNs. quBO uses only one - ubo.
I am not saying quBO is perfect. I surely don’t like that it duplicates data from one qube to another, but since it is not possible to have independent volumes attachable to qubes, I have no better solution for the moment.
See also: