Round vs. Square Backers
I've used them both, in plastic and aluminum. I don't see that big of a difference in terms of durability, but you don't notice when the round ones spin in the track, if the stud loosens up. If you're anal retentive about installation and placement, you might like to have things squared off on the track, so they are all equal. It kind of bugs me, but not that much. Other than that, I don't see a benefit, unless you want color.