I actually have one and use it all the time, I've found that you have to hold your chain still in the tool and not rely on the clamps and tool to hold it steady , rather you hold it by hand so the angle doesnt change, Ive been more than impressed by it and would buy another. i talked to a friend of mine who has a commercial shop and uses the commercial versions and he says you have to hold them with all of them that over time they get sloppy , I know someone will disagree but I like mine , its a 35 ,oo dollar sharpener that's paid for its self 10 times over and i can consistently get a sharp chain with it , like any other tool its only as good as the person running it . as far as sharpening with a file forget about it , mine always cut circles