Ive run all kinds of diffs in all kinds of vehicles.
Id rather have to tune a ball diff than a gear diff on race day. Esp when running multiple classes. Pop off a link insert allen wrench and done - vs a tear down and rebuild...
A ball diff car feels way more consistent, period. Better in turns and runs a straighter line down the (ahem) straight.
Im running an rtr b4.1 and cant wait to get my hands on a FT car. Just cant find them (new). I have it set up as close as i can to a team spec, but a team car is going to work better with these settings. Mainly due to shocks and a ball diff. I just cant trust this gear diff in the corners. It seems to let loose at inopportune moments. I have it tuned as well as i can with oils but it simply is not the same. Very unreliable in the corners, running the same lines and throttle control.
The mechanical make-up of the diff is where its at.