I have had one for several years in the front 60 on my K5. Before the Lock-Right I had a limited slip in the front and really did not notice much difference in turning ability, though the capability went up dramatically.
I have never felt the need to unlock one hub on the trail. I have used 2wd a couple of times for turning purposes but only when on an easy section of the trail that just requires some real tight turns. While there is a difference, I don't think the difference is huge in regards to turning ability. If it's a hard enough part of the trail that you can't easily do it in 2wd and therefore have it in 4wd, then I've never had an issue with the front locker. I've seen people with selectable front lockers (ARB's, etc...) try to turning them off on an obstacle that also requires a tight turn, and they just seem to beat on the rig harder to try to make it.