I'm probably arriving a little late to wade in, however I might be able to help u with the lokka's. I've had a fair bit of experience with air lokkers (also electric and vacuum lokkers) and like the boys say, they are great and they are also fairly cost prohibitive unless you plan on using them in comps etc., cause lets face it if the vehicle is otherwise un modded or only slightly lifted, the places you need to go to use twins will break your car (read 'the claw' at cruiser park etc).
I have fitter a 'lokka' (auto lokker) to the front diff of my ifs hilux and it has improved its ability no end (for $700 bucks). Bear in mind I bought this ute for touring and not club/comp work. Spose what i'm trying to say is take it from someone who has modded numerous 4bies, and decide what u want to do b4 u start shelling out big bucks.
Also - what type of vehicle have u got? Cause some makes hate lokkers and will start spitting c.v's etc when driven hard - my lux for example, and the 100 series before that, and the 80 series before that. Probably opened a can of worms now........ see ya