RE: OFFICIAL HPI RUSH / EVO THREAD
The cast metal ones sure are a great replacement when stripped the pot ones. I also got them when I stripped the pot metal gears. Although I use them as a back-up diff in case my ball-diff screws up, they are still going strong. I also think the ball-diff in combination with the HD middle gear is bullet proof, the only downside is that you can't get the outputs seperately, so you'll have to get a whole new ball diff [:'(].