When I read about the buttonhole cast on as described in The Knitter’s Handbook, my first thought was, “Huh?” It’s a weird cast on that’s basically a series of knots. You make a loop as if you were going to backwards loop cast on, but you pull a strand of yarn through that loop with your needle to create the knotted stitch. The knots are a bit like slip knots, and you have to adjust each knot as you make them to make sure they sit close to each other on the needle without a lot of excess yarn in between.
I was surprised by how nice the edge worked out when the stitches were adjusted just right. It’s not rigid, but it’s also not ridiculously loose. It’s not too bulky; it’s stretchy; and it snaps back to it’s original width easily.
When used at the end of a row, it has the same loose stitch issue as most of the other methods, but if you’re picking up stitches, it isn’t a big deal. So would I use this one? Nope. Adjusting each stitch takes forever. It’d be fine if you were casting on two or three stitches for a buttonhole, but it’s too much work for necklines or underarms.