The diff guards seem to work well and don't have any clearance issues. The Barnett cover might not look the coolest, but you'll see that it provides you protection in the area you need it the most, while not interfering with space at the top of the diff cover where you'd run into issues with track bar clearance and other things.
Even the Metalcloak track bar is not immune to the clearance issues encountered by the ARB, Riddler and other diff covers. Currie is one of the best track bars for clearance out there, and even it has issues with clearing most of these differential covers.
I think most of these differential covers aren't made with clearance in mind. Either that or they're testing them on rigs that have massive amounts of bump stop or other worldly custom steering setups and such.