I use them mainly becauae I wasnt sure of how much to crimp the other type and I was new to rig making. Ok the tool is a few pennies and they do seem a little more expensive, but yes you can move them and I have no idea about "big" fish as I havenet caught anything of any size on them, but flatties, schoolies etc are no problem. nothing moved..
I use them myself and find them really handy to keep clipped down rigs streamlined for casting as you can adjust them if you get any snood stretch. I think the tool is a bit of a gimmick as I have used both the tool and a normal crimping tool I already had and had the exact same result. Again, I've not had a large fish on one to move it yet, but I am thinking, even if it does, you can just move it back when re-baiting.