I have not tried the zigzag method but am happy with two rows of the largest style stitches then pullling the bobbin thread to gather. I just learned about sewing the two rows on either side of where the seam is- this seems to help a great deal in making nice even gathers that don't push over to one side too much.
I do this when I am making nice dresses or other "good" things, but so far the zigzag method has been working. I have found it necessary to anchor the starting end of the cord...
My serger is not healthy... I am afraid it may be terminal. When I get a new one, I would like to learn to gather with it.