Mini-Spool ties the rear tires to ALWAYS turn the same amount in relation to each other. Lockrite does allow ratcheting so that you're not hopping everytime you go around a corner.
I've got the spool in the rear of my '87, with 31x11.50 baja claws, and no complaints. I don't drive it on the road, locker-bang makes me uncomfortable, and you can't beat spool-traction for the price, unless you're comfortable taking the time and knowledge to weld it yourself.
If it's a street rig, I wouldn't suggest it, or at least not if you aren't running cheapy-tires.