A person I know has them on his ride. I would steer away from them immediately. Use them only if you will be using your 40 series as a trail rig. On the road, under power, you never know when they lock. Although, this is what I will be getting this year for sure for my Pajero.
LOKKA - Automatic Differential Locker
Slightly different than an Aussie Locker. The Aussie's will lock only when you lose traction, the Lokka on the other hand will always be locked except when you turn etc. Its nearly the inverse of traditional automatic lockers.
People love the Lokka. Of course there is a down side, harder steering, engaging / disengaging noises when you turn etc. But, the only thing holding me back from ordering one is not knowing who will install it for me.
Check it out.
PS. If i had a 40 series, I would just change the differentials, why would you want to mess with auto lockers etc when you can have a true rear and front locked differential??