Works great, not so durable
First, mine broke after a few uses. The plastic snapped on half on one side, allowing the file to simply fall out. I kept it in my closet when not in use and did not carry it with me, so I am inclined to believe it was poor construction. Some marine epoxy later (amazing stuff) and it works again. I filled a fair amount of the ribbing with the epoxy to strengthen it against future breakage.
That said, it works great. Much easier and more precise than a plain file, much less expensive than a professional edge tool. My edges are pristine now with very little work.
I can't wholeheartedly recommend it because it broke so easily, but when it does work it works well.