Clutch types have a clutches on the out board sides of the axle spider gears stacked up usually with a z shaped pre loader spring putting tension on the clutches behind the gears.
The locker type that stink look like the guts to a grandfathers clock and has a locking pawl spring loaded that locks the carrier in posi traction when needed. This is the weak link in this unit.
The better choice for racing looks exactly the same as an open carrier but with the clutches on the outer face of the axle spider gears with the pre-load spring that creates static tension on the clutches the axle pinion retains when installed.
Some 7.5/8" units and some others have cones instead of clutches and are not preferred for racing applications either. The cones wear out fast and make chatter when they slip like a clutch type can without the friction modifier in the gear lube.
Bruce