I’ve had one in my Dana 35 for almost year now. I liked it so well I got one for the front. The rear took about 2 hours going really slow, but I had never seen inside a differential cover before. The front was a little harder because I had to pull the carrier and separate the ring gear. It took about 6 hours, but it was very leisurely with several breaks for smokes and beer. You can buy the rear Lock Right for about $250; the front is a little more expensive at around $280. DO NOT pay someone to install them! If you can change your oil then you can do this. Occasionally the rear will pop/bang (most when backing up), but it’s not nearly as bad as people make it out to be. I’ve never heard a peep from the front, but it does make it steer a little differently in 4 WD. For the $500 he is quoting, you can buy the front AND rear and install them yourself. I only have 31” ATs on my XJ and I’ve gotten into places where guys with 35” MTs can’t.