I also use the JB Custom Fabrications kit. I love mine. I keep my hubs locked on the trail, but not around town. It's nice to be able to easily disengage the front axle on tight sections of trail. It really stops the "push" you get from a front axle with a locker.
There is an internal interlock that prevents you from having one axle in high range and the other axle in low range at the same time. Unfortunately, the way it works it also prevents having the front axle engaged without the rear axle engaged, so no FWD. Removing it does require some disassembly of the T-case.
The advantage is theoretically being able to drive in front wheel drive (only) if you mess up the rear driveline. I figure most situations where that is conceivable, I can just remove the rear driveshaft and limp somewhere on the front axle only, letting the rear T-case output spin without being connected to anything.
There is also a maneuver called a front wheel dig--you can google to see videos. Never done it, never needed to, but having front wheel drive only (and rear brakes) is the prerequisite.
I'm pretty confident I wouldn't forget and screw up, but I worried that anyone who ever drove my Jeep could accidentally get it wrong and destroy something. I left the interlock pill in, even when I had the D300 fully disassembled to put in a 4:1 kit. Risk wasn't worth the reward for me. Others will disagree, I'm sure