Crossbars question

A lot of the "prinsu design" style roof racks I'm seeing seem to use standard 8020 crossbars, either 2" or 3" wide. And then some just use their own style... which I'm not sure I love the idea. Proprietary and more costly.

I noticed the Greenlane offroad rack using a standard extrusion, but it's not the typical square ones:
https://images.squarespace-cdn.com/...69TlCeE0rAhj6HUpXkw/IMG_0416.jpg?format=2500w

My first thought is you have the exact same top slots, but lose the side+bottom slots. I'd also wonder if, being non-square, the rigidity of it would be less? I don't know enough about this stuff...

My main question though is: For those of you that have those aluminium extruded crossbars, how often are you using the side or even bottom channels of a crossbar?

 

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