For many many years now, ARB has been dominating the air locker market here in North America, They now have a little competition.
TJM has now brought their products line to the United States rivaling ARB, not only in Air Lockers but in Air Compressors,  Bumpers, suspension, lights, recovery equipment and other off road equipment. TJM Lockers are available immediately online at Rugged Rocks and other TJM products will be listed soon. The TJM Products listed online can be viewed at: http://ruggedrocksoffroad.com/tjm-m-474.html
In the last few years ARB has been good to the Nissan crowd listening to our needs. After many conversations with the tech department and after much debate, ARB has decided to build R180 front differential lockers the 05+ Xterra / Frontier. These are currently available for pre-order and are expected in stock in early march. Order now, Here: 
Some ARB air locker applications require that you change the OE carrier bearings to a slightly different carrier bearing.