They really are, especially for an only one or two time use. However, if the nut is already cut to the right height, you could simply wrap a piece of light grit paper (1000 should be abrasive enough) around a string (best to use the adjacent, thinner string for this - for instance, the A string for the E slot) and give it a straight pull through. This should remove any snags and then you can add some graphite as Dad suggests.