Kev, I've run EZ lockers on several different vehicles (Blazer, Cherokee, Toyota and K10 Pickup).
The only thing that's happened a couple of times is that the limit pins have broken inside, causing it to not lockup. The good side to this is the fact that simply replacing the pins (still requires tear down, etc.) is that the pins are cheap, vs. getting a new locker.
Some guys don't like the limit pins, but I think Dollars to doughnuts they're the best bang for the buck.
The only time I broke the pins was when I was either hot-doggin' or otherwise stupid. Consider full throttle in a '76 K10 full size automatic, massive wheel spin with 35" BFG's, going
up a muddy hill and then hitting dry ground on the other side, fairly stupid!
*Sidenote: Chicks only dig body damage if they don't have to walk 1.5 miles off a muddy, cold and hunter heavy wooded mountain 40 miles from home. Just a lesson I thought I'd pass on there.
Needless to say, yanking the EZ to put pins in 'er was the least of my worries. Getting a new gas tank in after towing it to Glenwood Springs from Colbran was the biggest concern.