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Maybe he doesn't want to have to use any accessories/hubs?

His reasoning turned out to be that he couldn't find a hub that didn't require external power but this will always be the case if you have a lot attached to it. But I have used a USB-C hub with HDMI and a 500GB SSD attached to it with my 12.9 Pro without attached power to the hub. In this case, it will draw power from the iPad.
 
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