Sometimes it doesn't matter if it slants L or R, a kfb doesn't. But they're not the same. Kfb uses a stitch and M1 puts the new st between 2 existing ones without using them. You can do a backward loop on the needle for m1, don't pull it tight and it won't leave a hole.
If you have a row that starts with 9 sts and you k3, m1, k3, m1, k3, and you use a kfb it would go - k3, kfb, k3, kfb, and then there's only 1 st at the end because you used up the other 2 in the kfb. You can substitutie it, but you have to work the sts a little differently - k2, kfb, k2, kfb, k3 and that works
sue- knitting heretic