Some info re spools and welded lockers.
A welded diff centre basically behaves the same as a spool centre, they both provide a way of giving direct drive to the rear axles.
They both also put lots of load on the rest of the driveline, especially gearboxes and axles, the problems usually show up if you are thrashing the car through tight left then right corners where lots of steering lock is required. When you hear things like "you get axle wind up" then those loads have to go somewhere and it usually transfers the loads to other driveline bits. Ever herd the common "wanted to buy" AXLES because someone runs a locker on the street
As for having to replace both axles if you break one with a welded centre - what a load of sh1t. You weld the diff centre not the axles
All this points to why manufactures put LSD's into production cars, they are usually a way of transfering power or torque smoothly and progressively without sending large shock loads to the rest of the driveline.
I can not understand why someone would buy a spool when a cheap welded centre will do the same thing.