I believe Michal is running the traxide (?) one in his LR4.
I don't have a preference for one brand over another. You can build your own for a lot less than any of the pre-made kits, but they often include extra bells and whistles. DIY you have less than $100 in parts (not including a battery). I don't run dual batteries on my trucks since I don't stay base-camped in one place long enough to need them even with a fridge. I have a suspicion that a lot of people put them in and don't actually need them, but they certainly don't hurt anything. At least as long as they're installed correctly... I seem to recall spending some time trying to figure out some wiring issues on Michal's installation in the middle of the Mendocino Forest last year - I don't recommend his installer
Basically it comes down to how elaborate you want to get. The first one is fairly basic; it's basically what I would build if I were doing one from scratch. It has some extra options like a battery monitor as well but isn't vehicle specific. The second one is made specifically for the LR3 and has all the wiring cut to length already as well as a factory battery tray, terminals, etc. It's pretty much plug and play and has more features but at a higher price. One worry - I don't know where you mount the 2nd battery in an LR4 as compared to an LR3, so it may or may not bolt straight in.
If you wanted to build your own, you just need to figure out a battery mounting location then we can wire in a simple hi-current continuous duty solenoid. They are generic; nothing special about them. Probably $35-45 from Amazon. Then make up some battery cables and you're good to go.