The Lokka is a locker.
ARB air locker is a selectable locker, and the Lokka is an auto-locker.
I will discuss the 2000 - 2004 X applications:
The ARB is available in front and rear diff versions.
The Lokka, for the X is only available for the FRONT diff.
The ARB, being selectable, can be turned OFF, even in 4wd. If you switch it this way, you can even use the rear ARB when in 2wd, etc.
The REASON you might WANT to turn OFF a locker in front, is that its harder to STEER when the diff is locked, as, the sides can't differentiate when locked.
So, with the ARB, if you are in a tight turn, in 4wd, you can can turn off the front locker, and more easily turn.
Of the available auto-lockers, the Lokka turns the EASIEST, as it DOES allow differentiation when locked. In 2wd, its invisible...as in 2wd, there's no input from the diff, and therefore no input from the Lokka.
When engaging, the Lokka needs less rotation than the other auto-lockers (lock-rite, etc), which are structurally VERY similar looking, but which, in the field, make more ratcheting noises and wind up the drivetrain more, etc....because they need MORE rotation to differentiate.
So, the Lokka will make ratcheting noises in tight turns when in 4wd, but not in 2wd or on less tight turns, and, it works great off road. Its relatively easy to install, and, is far less expensive than an air-locker and OBA system to run it, etc.
If you spend the $ on the ARB, you gain the ability to turn it on/off when off road...and it too is a proven entity that works great. If you wanted an OBA system anyway, you could rationalize away some of the cost differences related to the OBA needed to run the ARB air-locker, etc.
Every one I know who HAS the Lokka loves it, and, for the 2000 - 2004 at least, snowy roads doesn't seem as much of a problem in 4wd as the other auto-lockers have. I don't actually KNOW anyone with a 2005+ X with the Lokka, but I have heard that the 2nd Gen X's have a front diff set-up that might make the lokka have input even when in 2wd...but I don't know of anyone with the set-up to confirm that...or what that's like.
A locked diff, regardless of why its locked, or even an LSD, doesn't differentiate AS WELL as an open diff...and, there are always some quirks to the resultant handling that you'd want to familiarize yourself with.
Obviously, there are people who even drive around with welded front and rear diffs...but, to me, that's a bit too mad max.
An ARB when locked, cannot differentiate AT ALL...so, steering a locked ARB IS ridiculously difficult in a tight turn...so people, sometimes need to unlock it to make tight turns. Steering a locked Lokka is harder to turn than an open diff in a tight turn, but not near as bad as a locked ARB would be...and, you can always just shift into 2wd to unlock it.
Fromfrontier -
You have a 2nd gen with the Lokka, and, I would be interested in your input and experiences thus far.
ANY locker is a new driving experience: is this your first locked rig, or have you done this on other rigs before, etc?