i have an ARB air locker in the rear of my 100. A few points.
positives:
1. The locker itself is awesome and you really notice the extra traction
2. I have the ARB compressor that also pumps up tyres and it is also a great bit of kit (as long as you don't lose the tiny little piece of steel that clamps it to the tyres....)
negatives:
1. I have had the o rings replaced under warranty (you will know you need this when you get diff oil back up the air hose line...), apparently an install mistake
2. Then the entire rear diff had to be rebuilt after noticing a heap of metal shavings on the magnetic sump plug. To ARB's credit though, they did it all under warranty and without fuss.
3. the air hose into the rear diff itself is plumbed into the side of the diff house (pumpkin). Apparently this is the only way to do it on my vehicle. The problem is that i have had tree branches flick up and rip the hose out which means no air pressure which means no locker and no ability to re-inflate tyres.
so - i would ask about how the air hose is tapped. If it is in the side, then go an elocker as there is an unnecessary risk of failure . I would go an elocker anyway but if you do go pneumatic, then get it installed by someone who will stand by the install warranty.
