It's an open front diff (as Peabody just said) so if you're really stuck and you mash the fun pedal you'll have one-wheel peels on both axles. But it does make a huge difference anyway.
The "other" ones look like Chinese junk to me. If you want something cheaper than the Warns, hit the boneyards and find a 4x4 Mazda B-truck (one of the brick-shaped ones before they turned them into a Ranger with upside-down taillights), the manual hubs on those are a direct bolt-on if you have the awful vacuum hubs, though you have to swap the axle nut and retainer if you have the centrifugals.