I run old GPM ones in mine, they were steel and unbreakable. I think the current ones might have an alloy bone. It replaces the kit shaft and axle stub and allows you to retain the big gearbox outdrive (that you were previously losing all the time). If you were to go with a proper Tamiya CVD you'd need to replace the gearbox cup with a smaller metal one, I use M05 Mini ones on my full race TT02S as they're cheap and easily available.