i received mine couple weeks ago and it works like a charm... practically foolproof, just have to measure your carto once and adjust the left screw and then punch it by turning the top one.. you can't see clearly on the pic, but there's the screw is actually tapered slightly and once the tapered edge "lines up" with the bottom lip inside the viewing hole, know that's when to stop.
course, if you think that the hole is too big, then don't screw it all the way down. it's pretty adjustable that way.