I guess I am more of a traditionalist. I have seen lots of challenge/commemorative coins and the majority of them have been round.
I would think making the CVO coin round ,it would be easier to make and you could balance the designs for the front and back easier.
If you made the coin round you could easily expand the gold outer ring to the top edge so it forms an outer ring very easily on the front.
As far as the back if you made the coin round you could easily expand the globe and the overall shape would match the design of the actual coin. It would also give more room for the globe/eagle/engraving space.
It would also eliminate the design "dead space" created by the backside of the wings vs. the diameter of the globe.
Then a round coin would be easier to carry in a pocket by not having edges to dig in on a long ride. Most display boxes and shelves for the challenge coins are designed for the round coins , so for those members that may have other type of coins, the CVO coin will fit into their collections.
But this is just my .02.