This is one of those techniques where I read the instructions and think, “Weird.” Naturally those always make it on my list of things to try. The Increase Button Hole is made by binding off a bunch of stitches and then working a couple YOs after the BO. On the next row you drop the YOs and stretch out the last stitch before the hole using the yarn from the YOs. Then you work a bunch of stitches into the front and back of the giant stitch to replace to BO stitches. Weird.
The Increase Button Hole is a bit less bulky than the One Row Button Hole and a bit more stretchy. It does gap a little, but it’s not too bad. It would be a good button hole if you wanted to a use a medium or large button but didn’t have a lot of stitches to bind off like the One Row Button Hole would require.
My only complaint is that the top edge is lumpy and bumpy from working into the front and back of the big stitch to increase. It makes the differences between the BO and CO pretty noticeable.