Those are pretty cool! It seems to me I looked at some commercial options like that a while back.

They certainly would do the trick for a bar bag and accessories - like a phone mount (RAM maybe with a long arm), bell, etc. However, they will not work for a mirror to get your view around your gear on the back. You may be able to modify it with an extension out of one side or the other (left makes most sense, unless your country has traffic on the left side of the road instead of the right) to mount the mirror to.

More food for thought.