Answers,
Auto Hubs Suck, they break easier and unlock
when you don't want them to.
Lockers allow the diff to let one tire turn different
speed than the other, yet when both wheels spin
the same speed locks the axles together as if it
were a spool.
Spool eliminates all spider gears and just puts the
power to the ground with no differential effect, also
breaks axles if you get big tires so a spool is not
good for on road use.