Shape of the bearing adjusters vs. rectangular bar stock

I was looking at the bearing adjusters and wondering if there was any advantage to the round shape with two flats vs. just a rectangular piece of aluminum with two holes. The round shape is more aesthetically pleasing but I was thinking that it would be easier to build for those without access to a milling machine if it were made from bar stock. Also, is there any advantage to using 1/2" bar stock and then adding round 1/4 spacer vs. having to mill? Thanks in advance!