If you use kfb instead of m1 you may not come out with the right number of stitches or the increase will be in the wrong spot. Kfb uses a stitch but m1 is between stitches; on some patterns it doesn't matter, such as if you inc at the beg and end of a row. But in this one where it's k2, m1 all across the row, if you k2, kfb you wont get the right amount of stitches. When you do sub it, you need to know that kfb would be k1, m1 so on this pattern it would be k1, kfb all around the stitches.
sue- knitting heretic