The gear diff is superior in acceleration since there is no slip. It also offers more steering than a spool without the violence associated with getting on and off the throttle. You can also correct the car more easily coming off the corner.
The gear diff is more a tuning item than a way to avoid maintenance, since you have to keep up with them as well.
These are just my feelings, and I usually only race motors up to 17.5 boost, so your mileage may vary.
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