I've used one for several years. I'm a geek so I decided to test it out before using it. I slipped something (can't remember what) in the cuff so that there was only one layer and then ran the rotary cutter over the just the wrist part a few times. The yarn fibers were cut a bit but the wires didn't let the blade cut through at all.
I wear it only on my left hand since I'm right-handed, being sure to retract the blade on the cutter before setting it down between cuts. This leaves my right hand free to move the fabric or whatever.