Re: 2012 Overland question
They don't make a front ELSD for any 2011 or 2012 JGC model. The rear ELSD is currently available only as part of the Overland ORA or Summit package. It was more widely available in 2011.
If you are new to off roading, you probably wouldn't notice the lack of ELSD unless you routinely ride with a rear tire off the ground, in deep mud, sand, or in heavy snow. Things you shouldn't come across much on moderate trails or rarely on easy trails. You will have brake traction control to reduce wheel spin regardless. ELSD allows more power to be directed to the wheel with traction, most useful in the more challenging trails and heavy snow/mud conditions IMHO. Lockers are perferred, of corse, but they take a bit more skill to use. Us amateurs have a tendency to forget to disengage them and get ourselves into trouble. If you do a lot of off road with wheel spinning, the ELSD will reduce wear and tear on the rear brakes.
ORA also includes skid plates, tow hooks, and 18 inch tires, which are a significant benefit when off roading (if you go clubbing tow hooks are typically mandatory). You can install these pieces yourself, but the tow hooks take a lot of work.
There are many moderate trail runners without ELSD and they do just fine, the JGC is pretty capable as is. If you want to ride the more challenging trails you may want to think about a different model Jeep. Ground clearance and tire choice, along with driver skill will make much more difference than an ELSD rear IMHO.