"According to the video Paul linked above with the expedition(?), the TrueTrac can only be 'locked' from a full stop by holding brakes while applying a little gas. Wheel spin seems to disengage the lock as described in that video. This does present some complications for a manual transmission driver, but that's one reason I have a hand throttle."
Yes....the electronically sensored LSDs (and lockers in some cases) require a certain amount of differential wheelspin to engage. The standard collection of aftermarket LSDs and lockers you are considering won't have that issue. But even then, trying to control wheel spin is an issue with an LSD...Apparently better drivers than me are able to apply some braking to control the rear wheel spin and get the LSD to bind more while also working throttle and clutch....I've never had any success with it on either of my LSD equipped jeeps that were manuals, hand throttle or not. Granted, my old cjs have other issues with trying to drive through the floor pedals and mechanical non-power pedal controls etc - so maybe on modern vehicles it would work better. Although I cannot do it with the old cj5 due to my parking brake set-up mounted on the transfer case, I know some people can use the parking brake a few clicks on their rear brakes to help control wheel spin and keeps your feet free to do normal things. I think in an automatic set-up where you drive one foot on light throttle, and one foot working the brake pedal to ease forward, it has a better chance of working as well....
But it also comes down to an LSD is what it is...it is a nice improvement in traction over an open differential, and works well in loose or even slippery conditions where you keep the tires on the ground. But an LSD is a 'limited slip', it limits differential wheel spin, but doesn't stop it. In other words, its just not the same as a locker - it won't give traction once one side is unweighted/lifted and spinning no matter how fancy you get with your foot and brake work. Only a locker (whether auto, selectable, spool) will work in that situation. After running two different jeeps with LSDs, I got my first true locker in the tacoma - and it was a different world. The only thing that limited my tacoma was its clearance with long wheel base and no lift. And it made me realize the cj needed a locker, and when I swapped out the LSD to the e-locker in the cj5, well, that jeep almost keeps up with all of you with modern built jeeps today. The traction gains are just orders of magnitude greater than an LSD. I think there is/was some old threads on the forum that talked about what is most important priorities when building a 4x4....We all like more lift and bigger tires etc, but in many ways, there is no bigger bang for your buck than a locker, and yes that is a lot of buck, but the bang is huge.
But again, that doesn't make a locker the right choice...As you have said, its more about building a jeep that matches your intended usage goals as opposed to just maximizing traction. I think the gear driven LSDs are solid, reliable and aid traction - the clutch driven LSDs just aren't worth the money and maintenance IMHO. Certainly if you go the LSD route, you probably consider running both front and rear, especially given all the sunk expense of the regear front and rear. With dual LSDs, you will notice a very big gain in traction over your single rear, and probably worn Trac-lok. The old saying is 2 LSDs = 1 locker.....I actually think a single rear locker is more valuable than 2 LSDs, but its close, and may also depend on the type of trail you drive on. Paul said it best - front and rear gear driven LSDs on the long wheelbase LJ will get you almost anywhere that isn't lifting tires in the big rocks. Probably an ideal set-up for what I envision when you talk about overlanding across the southwest. But the other side of the discussion might also beabout cost - the majority of the cost at this point is in the gear set up labor, so would using a selectable locker in the rear add much cost over an LSD? There is zero downside to a selectable locker (there is downside to an auto locker), only upside and a bit more expense. It will do everything the gear driven LSD will do and more, meet all your overlanding needs, and still have some additional capability for when following Shane into something stupid because he has portals! And of course, I would still suggest the gear driven LSD in the front - that would be one helluva a set up. Maybe thats why I will be going that route - well actually i am going that route because no selectable lockers are available for my front end, but I am expecting it to be one helluva set-up!