I've got Lincoln Lockers front and rear in my YJ and I love 'em. Wouldn't have it any other way. Sortof a poor-jeepers spool, if you will. There is no spool or mini-spool available for the D30 and D35 so welding was my only option.
Mini-spool replaces the spider gears and uses the stock diff carrier, locking both axle shafts together.
I actually think the spool or lincoln locker is easier on axle shafts than a part-time locker, when on the trail. When a part-time locker locks during wheel spin, that's a lot of shear force on a narrow axle shaft like a D35, seen a lot of them snap during this. No guesswork with a spool, it's always locked so less chance of shearing an axle shaft in half.
A posi is the same as a limited slip, it biases torque between the two wheels and is better than an open diff, not as reliable for traction as a locker. Limited slips are nearly transparent when driving on the road, and I've seen them do very well offroad.