I installed the Riddler diff cover because the one I originally wanted (the $64 SOLID) cover was out of stock. I was looking for alternatives that didn't cost $170 like the ARB cover and this came up. I found at Jeepforum vendor for $99 shipped which was a great price. Another thing that compelled be to buy it: the Youtube review where it is destroyed using extremely heavy machinery.
The cover comes unpainted but coated in oil to prevent rust. Before installing, be sure to clean it thoroughly. I also heated mine up with a torch to evaporate any oils that had soaked into the porous cast iron. I painted it with Rustoleum Professional Enamel in a spray can and it is holding up nicely, even being dragged through dirt and bounced off rocks.
Other reviews mentioned weak stainless hardware breaking as you torqued the bolts down, but mine came with Grade 5 zinc-plated bolts which had no problems at all. I paired it with a Lubelocker gasket on my Dana 30 and it is 100% leak free.
To date, I have dragged it through rocky dirt in a really rutted area and bounced it off a rock, no problems, barely even scratched the paint.
I've read that TJs sometimes have clearance issues with the Riddler diff cover around the track bar at full stuff. No such issues on my WJ, both with the OEM track bar and with the JKS track bar. It also sticks a little further forward and comes close to the tie rod at full steering lock. However, there's still enough room to get your finger between it and the tie rod, and even more room with the JKS tie rod installed (smaller OD than stock).