Let me just drop drop my 2 cents here, Skip to the 3rd paragraph for the summary
I have a Lunchbox locker on my front axle due to me not having time to wait for a selectable (Plus its about 1k for one) and amazon had a sale and Amazon being amazon i got free overnight shipping (Cause amazon prime) and it made it in time for an event and so far about 32K miles on it and counting and about 100 miles of rocks on it ? if that makes sense ? Its been great!
CONS: But for the money (at the time,close to 2 years ago) i paid 130 bucks for it and i love it! However....When your in tight technical trails i really wish that i could have a selectable locker at times since it locks up under load/Or when your on the gas(its the lockers normal nature) and welp...whenever you gotta back up and go foward a few times and You can't just simply put it back in 2wd due to what your jeep is on It kinda tends to suck and the "peer pressure" kinda hits

when a crowd is watching . You gotta be set on a line and go for it!
But either way for what you'll pay for i'd say its worth the money even with its quirks And you got a great source of traction for cheap,Just take out your axle shafts(and the other parts to get to the shafts

) carrier and ring gear out, Take the spider gears out and plop in your nice new Spartan lunchbox locker and bam ! You got an auto locker

no need for shims since you're using stock stuff and Putting it back in! But yeah once i actually build my rig, It'll actually have a real selectable locker !